In a large pot or dutch oven over medium-high heat, brown ground beef with the red onion and garlic, about 15 minutes. If you're meat was fairly fatty, drain out fat, leaving 1 - 2 Tbsp of rendered fat in the pot.
When the meat is browned, add the butternut squash, carrots, red and green bell peppers, diced tomatoes, tomato paste, chili seasoning and beef broth to the pot, and stir.
Bring to a boil, then reduce heat and simmer uncovered for 2 hours. The butternut squash should be fork tender.
Garnish with chopped scallions, and serve.
Notes
If your chili becomes too thick, add more broth until it reaches the consistency you want.