In a large soup pot, heat oil over medium-high, then saute onions, bell peppers, and garlic until the onion and garlic begin to brown, about 5 minutes. Reduce heat to medium, add tomatoes and cook, stirring from time to time, until they cook down, 5 to 10 minutes. Pour in tomato juice and broth and add black pepper and red pepper flakes. Bring to a boil over medium-high heat, add rice, then reduce heat to low. Simmer, partially covered, 45 minutes. Add peanut butter all at once, stirring until it melts. Bring soup to a simmer. Serve hot.