Pat the chicken thighs dry and season with salt and pepper on both sides. Heat olive oil in a large skillet or Dutch oven over medium-high heat. Sear the chicken breast-side down until golden brown (about 5 minutes per side). Remove and set aside.
In the same pan, reduce heat to medium. Add onions and cook until soft and translucent, about 5 minutes. Add garlic and bell pepper; cook another 2–3 minutes. Make sure the garlic doesn’t burn. Deglaze the pan with wine or broth, scraping up any flavorful brown bits.
Add in the San Marzano tomatoes (crush by hand if whole), oregano, basil, and red pepper flakes. Stir to combine. * I like to add about 3-4 tablespoons of parmigiana into the sauce for added flavor.
Nestle the chicken thighs into the sauce. Cover and simmer on low for 35–45 minutes, or until the chicken is tender and cooked through.
Taste the sauce and adjust seasoning as needed.Serve over spaghetti or linguine, topped with fresh parsley and grated Parmigiano
