Heat the olive oil in a large pot over medium heat. Add chicken pieces and cook until lightly browned and no longer pink inside, about 5 minutes.: You will notice a faint fruity aroma as the olive oil warms and the surface shimmers slightly, which signals the right temperature to add the chicken . This light sizzle helps create a golden exterior that adds savory depth to the soup, and browning rather than steaming concentrates flavor. A common mistake is using too high heat, which can burn the oil or brownings too quickly, so keep the flame steady and spread the oil evenly across the pot.
Add the diced onion, garlic, carrots, and celery to the pot with the chicken. Cook until the vegetables are softened, about 5 minutes.: As the chicken hits the hot oil you will hear it sing softly, and small brown crusts will form on the contact points. Those browned bits add complexity when they are deglazed later. Ensure that pieces are not crowded, or they will steam and not develop color; if necessary cook in batches. Cut one piece to check that the center is opaque and juices run clear to confirm doneness.
Pour in the crushed tomatoes and chicken broth. Stir in the dried basil, oregano, salt, and pepper. Bring the soup to a boil, then reduce heat and simmer for 20 minutes.: When you add these aromatics you will get an immediate lift in scent, a mix of sweet and savory notes as the onion softens and the garlic releases its oils. Stir frequently so the vegetables sweat rather than burn, and aim for translucent onion and tender carrot, which usually takes a few minutes. Avoid high heat that can scorch the garlic , which turns bitter quickly.
Stir in the chopped spinach and cook for an additional 5 minutes or until the spinach has wilted and the soup is heated through.: The pot should fill with a gentle steam and a layered aroma that signals the base is developing. The visual cue is softened, slightly glossy vegetables and a fragrant smell that is more rounded and sweet. If they are still stiff, simmer a touch longer; undercooked vegetables will taste raw and disrupt the soup's harmony.
Pour in the crushed tomatoes and chicken broth: When you add the crushed tomatoes and chicken broth the mixture will transform, turning into a bubbling, rich liquid. Stir to incorporate the browned bits from the bottom of the pot, which releases concentrated flavor. Pour slowly to avoid splattering, and use the broth to adjust the soup's body; too little will make it very thick, while too much will dilute the taste.
Stir in the dried basil oregano salt and pepper: These dried herbs will perfume the simmering soup, releasing their essential oils into the broth and harmonizing with the tomato acidity. Season lightly at this stage, because flavors concentrate as the liquid reduces. A common error is over seasoning early, so remember you can always add more later after tasting.
Bring the soup to a boil then reduce heat and simmer for 20 minutes: The soup will bubble energetically as it reaches a boil, and lowering to a gentle simmer lets flavors meld without aggressive evaporation. You want small, steady bubbles that indicate a controlled simmer, which extracts flavor and softens the vegetables further. Simmering too hard can break down textures and make the chicken tough, so aim for a low, even simmer and stir occasionally to prevent sticking.
Stir in the chopped spinach and cook for an additional 5 minutes or until the spinach has wilted and the soup is heated through: When the spinach hits the hot broth it will rapidly collapse and change to a vivid green, releasing a fresh vegetal scent that brightens the entire pot. This late addition preserves the leafs tenderness and color; cooking it too long will make it mushy and dull. A common slip is adding it at the start, which robs the greens of their texture and brightness, so add it near the end and give it a few minutes to gently wilt.