Cook macaroni according to package directions. Drain and keep warm. Cook ground beef with onion in a 6-quart saucepan or Dutch oven over medium-high heat for 4 to 6 minutes or until crumbly and no longer pink. Drain, if needed. Stir in chili powder and crushed red pepper (if using). Add tomatoes and beans; bring to a boil. Reduce heat to low; simmer for 20 minutes. Add cooked macaroni; cook for 5 minutes. Season with salt and pepper to taste.