01 - Lightly season the chicken thighs with salt and pepper on all sides.
02 - In a large skillet over medium-high heat, sear the chicken thighs for 2-3 minutes per side until lightly browned for extra flavor development.
03 - Place the sliced onions, bell peppers, mushrooms, and garlic in the bottom of the slow cooker, creating an even layer.
04 - Arrange the browned chicken thighs on top of the vegetable layer.
05 - Pour in the diced tomatoes, crushed tomatoes, white wine or broth, oregano, basil, thyme, salt, black pepper, and crushed red pepper flakes. Stir gently to distribute ingredients evenly.
06 - Scatter the capers and sliced black olives over the mixture.
07 - Cover and cook on LOW for 6 hours or on HIGH for 3 hours, until the chicken is tender and the sauce is rich and flavorful.
08 - Taste the sauce and adjust salt, pepper, or herbs if needed.
09 - Garnish with chopped fresh parsley and serve hot, optionally sprinkled with grated Parmesan cheese. Pair with crusty bread, polenta, or pasta if desired.