Heat 2 tablespoons olive oil in a large skillet over medium heat until shimmering.

Season the chicken thighs with salt and pepper. Add them skin-side down and sear until golden brown, about 6–7 minutes per side. Work in batches if needed to avoid overcrowding.

Remove the seared chicken to a plate and set aside. Reserve any fat in the pan.

In the same skillet, add the chopped onion, sliced bell peppers, and mushrooms. Sauté over medium heat until softened and lightly caramelized, about 6–8 minutes, scraping up browned bits.

Stir in the minced garlic and cook 30–60 seconds until fragrant.

Add the can of diced tomatoes and their juices, sprinkle in the dried oregano, and season with salt and pepper. Stir to combine and bring to a gentle simmer.

Return the chicken thighs to the skillet, nestling them into the sauce. Cover and simmer over low heat for 25–30 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the sauce has thickened slightly.

Taste and adjust seasoning. Garnish with torn fresh basil and serve over pasta, rice, or crusty bread to sop up the sauce.