In a Dutch oven, heat butter over medium-high heat. Add beef, red pepper and onion; cook, crumbling beef, until meat is no longer pink and vegetables are tender, 6-8 minutes; drain., Add the next eight ingredients. Bring to a boil; reduce heat to low. Simmer, covered, about 20 minutes; add zucchini. Continue simmering until vegetables are tender, another 20-25 minutes. Just before serving, sprinkle with cheese if desired.