Add the gizzards to a large pot and 1 quart [1 liter] of water. Add a tablespoon of salt, 1 teaspoon of black pepper, 1 teaspoon of oregano, and the bay leaf. Boil until the gizzards become very tender, which can be 60 - 90 minutes, add water if it becomes necessary to prevent it from drying out. A pressure cooker or Instant pot speeds up this step to about 20 - 30 minutes.: You will notice a developing savory steam as the pot comes to a boil, and the scent becomes meaty and herbaceous, a clear sign that the long simmer is concentrating flavors. The bubbling sound should be steady and gentle, not a violent roar, which helps prevent toughening. The visual cue is the gizzards losing their pinkness and becoming plump and soft, sometimes with slightly ragged edges where connective tissue separates. This step matters because it transforms tough tissue into tender meat that will absorb sauce flavors later. A frequent pitfall is rushing the simmer, which leaves the gizzards chewy; if you have a pressure cooker, use it to reduce time while still achieving tenderness. Keep an eye on the water level and top up with hot water to maintain coverage, because exposing gizzards can dry them out and create uneven texture.
Separate the gizzards from the water (set both aside). Discard the bay leaf.: When you drain, notice the rich, slightly gelatinous hue of the cooking liquid, which holds concentrated flavor and is worth saving for the sauce. The gizzards will feel firmer than when raw but yield slightly to pressure, indicating readiness. The liquid should be fragrant but not overly oily; skim if necessary. Removing the bay leaf prevents its bitter texture from creeping into the finished plate. A common mistake here is discarding the cooking liquid, which would lose valuable backbone for the sauce; instead reserve a cup or so for depth. Let the gizzards rest briefly so any excess liquid drains, making the next sauté step more effective.
In a large skillet or Dutch oven (caldero), heat the oil over medium heat. Add the chicken gizzards and cook and stir until any liquid left has evaporated and there's only meat and oil left in the pan. Stir in bell pepper, onion, and garlic. Cook stirring until the onion becomes translucent. Stir in tomatoes, olives, and half a teaspoon of oregano. Add the tomato sauce and a cup of the liquid from boiling the gizzards.: The moment the gizzards hit the hot oil you should hear a steady sizzle and smell a roasting aroma as any residual broth reduces. As the liquid evaporates, the pan surface will start to show golden spots on the meat, signaling Maillard reactions that deepen flavor. When you add the peppers and onion , the sizzling will change to a sweeter, sharper aroma as sugars release. Cook until the onion softens and turns translucent, which mellows its bite. Introducing the fresh tomatoes and olives creates a bright, tangy steam that cuts through richness. Adding the reserved cooking liquid is key because it reincorporates the concentrated broth, lending body and umami. A typical error is crowding the pan, which causes steaming rather than browning, so if your pan is small work in batches or use a larger vessel to maintain surface contact for proper caramelization.
Cover with the lid, and simmer until the liquid has reduced to half (about 7 minutes). The vegetables will be tender, and the sauce should be a bit thick.: Once covered, the bubbling quiets to a gentle murmur, and you should notice the sauce gradually tightening and clinging to the gizzards and vegetables. Steam escaping from the lid carries a concentrated tomato aroma, and the surface will show small, slow-moving bubbles when the heat is right. This reduction concentrates the flavors and improves mouthfeel, transforming a loose broth into a spoonable sauce. Stir once or twice to prevent hot spots and to check texture, because over reducing will dry the pan and risk sticking. If the sauce thickens too quickly, add a splash more reserved cooking liquid to soften it without diluting flavor. A common slip is leaving it unattended until it reduces completely, which can scorch the bottom and create bitter notes, so watch this phase closely.
Season with salt and pepper to taste. Add fresh cilantro, and remove from the stove. See suggestions to serve above the recipe.: At this finishing moment you should rely on your palate; the aroma will be rounded, with tomato brightness and herb lift. Tasting will reveal whether the dish needs a final pinch of salt or a touch more black pepper to balance sweetness and acidity. Adding chopped parsley or cilantro introduces a fresh, grassy scent, and you will feel the contrast immediately against the warm, savory base. Removing the pot from heat preserves the herb aroma and prevents it from fading into the sauce. A mistake to avoid is over seasoning at the outset rather than adjusting at the end, which can lock in an overly salty profile. Plate promptly so the textures remain ideal, and enjoy the layered sensations you created from such simple beginnings.