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. This step is optional but adds depth of flavor.
03 - Place the sliced onions, bell peppers, mushrooms, and garlic in the bottom of the slow cooker.
04 - Arrange the browned chicken thighs on top of the vegetable layer.
05 - Pour in the diced tomatoes, crushed tomatoes, white wine or broth. Add the oregano, basil, thyme, salt, black pepper, and crushed red pepper flakes. Stir gently to distribute the seasonings.
06 - Scatter the capers and black olives evenly over the top of 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 has developed a rich flavor.
08 - Taste the sauce and adjust salt, pepper, or herbs if needed before serving.
09 - Sprinkle with chopped fresh parsley and serve hot. Optionally top with grated Parmesan cheese. Accompany with crusty bread, polenta, or pasta if desired.