Preheat the oven to 350°F/180°C.: The moment the oven warms, you get the subtle scent of heat that primes the kitchen. A properly preheated oven ensures even roasting, so the peppers cook through without drying out. You may notice a faint warm air scent as it reaches temperature. One common mistake is placing the peppers into a cold oven which makes them take longer and cook unevenly, so always wait until it is fully hot.
Prep the peppers, slice them in half, and remove the membrane and the seeds.: As you slice, you hear the crisp snap of fresh bell peppers , and the bright green or red flesh reveals a glossy interior. Removing the membrane and seeds makes the cavity easier to fill and gives a cleaner bite. Pay attention to keeping the stem intact if you want a pretty presentation. A typical error is leaving too much pith which can taste bitter, so scrape the inside well.
Place on a baking tray or in a casserole dish, drizzle with olive oil and brush it all over the peppers. Season with salt and pepper. Cook in the oven until they’re just undercooked, about 10 minutes.: As the peppers roast, the oil helps their skin wrinkle gently and the exposed flesh softens, releasing a sweet, roasted aroma. They should give slightly when pressed but remain firm enough to hold the filling, that pliable texture is the cue you are looking for. If you leave them too long, they will collapse and become mushy, so watch the clock and test one at the 8 to 9 minute mark if your oven runs hot.
As the peppers are being roasted, prepare the filling. In a large bowl, combine the shredded chicken with buffalo sauce, ranch dressing, mozzarella cheese, garlic powder, and onion powder. Stir to combine.: While mixing, the bowl fills with a tangy steam from the buffalo sauce and the creamy scent of ranch dressing . The mozzarella cheese begins to tangle with the strands of shredded chicken , giving a sense of cohesion. Combining while the peppers roast saves time and ensures the filling is ready as soon as the vessels are. If the mixture seems too loose, the filling may slide out when baked, so add the cheese gradually to test thickness. Over stirring can make the chicken stringy, so fold gently to maintain pleasant texture.
Remove the peppers from the oven, and carefully fill them with the prepared filling. Return to the oven and cook for 5 more minutes, then place under the broiler for 1-2 minutes.: When you fill the hot pepper shells, they welcome the warm filling and you can smell the mingled spices. The extra 5 minutes in the oven lets the filling warm through and the cheese start to melt into the meat. The quick broil at the end gives a slight browning to the top, creating a toasty contrast to the creamy interior. Watch closely under the broiler, as a minute can change golden to burnt. A common slip is leaving them under the broiler too long, which can char the tops instead of producing a light brown finish.
Remove from the oven, and top with crumbled blue cheese and/or ranch dressing, and sliced green onions.: As the filled peppers come out, steam rises carrying a tangy, savory perfume. The crumbled blue cheese will slightly soften on contact, offering pockets of sharpness, while the sliced green onions add a crisp, herbal snap and a burst of color. Allow them to rest briefly so the filling settles and the toppings meld. One mistake is plating immediately without a short rest, which can cause the filling to spill out and make serving messy, so give them two minutes before moving to a platter.