In a large pot, over medium-high heat, brown ground beef for 3 minutes. Add onions, red pepper, green pepper, and jalapeno; continue cooking for 3 more minutes. Add mushrooms and garlic; cook for another 2 minutes. Stir in all remaining ingredients (except butternut squash and balsamic vinegar). Bring to a boil, reduce heat, and simmer (partially covered) for 15-20 minutes.
Stir in squash and cook for 5-7 minutes; until squash is slightly tender. Pour in balsamic vinegar and serve immediately.