Preheat oven to 375°F. Heat the oil in a large dutch oven or oven-safe pot over medium-high heat. Season the chicken parts liberally with salt and pepper. Brown the chicken pieces, a few at a time, until crisp all over but not cooked through. Remove the chicken from the pot and set aside.
Add the chorizo to the pot and fry until the chorizo releases its oils, about 3 minutes. Stir in the onion and bell pepper and reduce the heat to low. Cook until softened, about 3-5 minutes. Mix in the garlic and chili powder and cook for an additional 2 minutes, stirring occasionally.
Stir in the crushed tomatoes, tomato paste, chicken stock, potatoes, butter beans, thyme sprigs and bay leaf and bring to a light boil. Reduce to a simmer, cover, and cook for 10 minutes.
Return the chicken to the pot. Cover and transfer to the oven. Cook for 30 minutes.
Remove thyme sprigs and bay leaf. Taste and season with additional salt and pepper, if desired. Stir in the spinach until it wilts. Serve warm with crusty bread.