1. Heat a 12-inch nonstick skillet over medium heat until hot. Add the beef and cook, breaking into smaller pieces with a wooden spoon, until lightly browned, about 8-9 minutes. Transfer to a bowl and reserve.
2. Return the skillet to the stove and heat the oil over medium heat. Stir in the onion and garlic; cook, stirring occasionally, until slightly softened, 3-4 minutes. Add the bell pepper and cook 2 minutes. Stir in the zucchini and cook 2 minutes longer until starting to soften. Add the tomatoes and cook until just starting to wilt, about 4-5 minutes. Stir in the reserved beef and cook until hot, about 2 minutes. Remove from the heat and stir in the basil, cheese, salt, and pepper.