Under medium high heat, brown all the chicken pieces in the oil on both sides. Add the slab bacon pieces near the end and turn down the heat to medium low. Remove the chicken pieces to a plate and add the diced onion and garlic, stirring continually until soft. Now turn the heat back up and pour in the bottle of red wine, stirring slowly to scrape up all the flavorful brown bits. After a few minutes, add in the chicken broth and stir in the tomato paste. Add the thyme, bay leaf, salt and pepper and bring to a boil to release all the flavors. Turn heat down to medium so the liquid is just simmering and add back in your chicken pieces, making sure they’re pretty well covered by the wine mixture. Cover and simmer gently for about 1 hour. If using fresh onions, add to the casserole for the last 20 minutes of cooking. If using frozen, add in for the last 5 minutes.  While your casserole is baking, sauté the mushroom in butter until they give up their liquid, and add them at the end, mixing all the ingredients together. Serve hot with crusty French bread. Bon appetit!