Heat oil in saucepan over medium-low heat. Add onion, garlic, carrot and celery; cook, stirring occasionally, 25 minutes, until vegetables are tender, making sure garlic doesn't burn. Add beef; cook over medium-high heat, stirring to break up meat, 7 minutes, until meat is no longer pink. Add tomatoes, bouillon, Italian seasoning, salt and pepper; cook over medium heat, stirring, 15 minutes.
Meanwhile, cook rigatoni in a large pot of lightly salted boiling water until al dente, firm but tender. Drain well. Serve sauce over pasta. Makes 6 servings.