1. Preheat oven to 375°. Heat oil in a heavy-bottomed 4- to 5-qt. pot over medium-high heat. Season chicken pieces with salt and pepper and add skin side down to pot. Cook until skin is crispy and deeply browned, about 12 minutes. Remove chicken from pot and set aside.
2. Pour off all but 2 tbsp. cooking fat, reduce heat to medium-low, and add onions, garlic, and thyme. Cook, stirring often, for 5 minutes, then add potatoes and bacon. Cook, stirring occasionally, until mixture is well browned, about 8 minutes. Pour off all but a thin layer of fat.
3. Add mushrooms and chicken stock, bring liquid to a boil, and cook until liquid is reduced by one-quarter. Arrange chicken, skin side up, on top of vegetables.
4. Transfer pot to oven and bake, uncovered, until chicken is cooked through, about 20 minutes.