Mix kidney beans, black beans, Great Northern beans, tomato sauce, garlic, onions, and pumpkin puree into a large slow cooker.
Add pumpkin pie spice, chili powder, cumin, and salt.
In large skillet, brown ground beef over medium-high heat. Drain grease. Mix in red pepper flakes, onion, and garlic.
Cook until onion is soft and transluscent. Mix in green and red peppers. Cook additional 5 minutes.
Mix ground beef into slow cooker
Cook on low until the chili is hot: 1 to 2 hours.