Heat olive oil in a skillet over medium heat. Add onions and sauté until translucent. Add garlic and spices and continue to sauté to toast and develop flavor. Add diced tomatoes, peppers, chipotles, broth, peanut butter, and chocolate. Simmer for 10 minutes. Season with salt and pepper to taste.
Ladle sauce into a blender, puree until smooth. Note: You may need to work in batches, depending on the size of your blender. Only fill halfway with sauce. Do not over-fill your blender or you'll have a hot mess!
Season chicken with salt and pepper. Pan sear the chicken in a heavy bottomed hot sauté pan over medium-high heat until browned on both sides. Add to casserole dish, cover with sauce and braise the oven for 45 minutes to 1 hour.