Heat the olive oil in a skillet over medium-high heat. Season the chicken with salt and pepper, then sear for 2–3 minutes per side until golden brown.

Add the sliced onion, red and green bell peppers, mushrooms, and minced garlic to the bottom of your slow cooker.

Place the seared or raw chicken thighs or breasts evenly on top of the vegetables in the slow cooker.

In a large bowl, combine crushed tomatoes, diced tomatoes, chicken broth, Italian seasoning, dried basil, oregano, red pepper flakes, salt, and pepper. Stir well to blend all ingredients.

Pour the tomato sauce mixture evenly over the chicken and vegetables in the slow cooker. Cover and cook on low for 6–7 hours or on high for 3–4 hours until the chicken is tender.

Stir in the capers, then taste and adjust the salt and pepper if needed.

Serve the chicken and tomato sauce over cooked pasta, rice, or mashed potatoes. Garnish with fresh parsley and basil.