In a large pot over medium heat, brown the ground beef until no longer pink. Use a spatula to break up the meat as it cooks.
Add the diced onion to the pot with the beef. Cook until the onion is translucent and soft, about 5 minutes.
Mix in the minced garlic and cook for an additional 1 minute until fragrant.
Stir in the pumpkin puree, diced tomatoes, and beef broth. Make sure to mix well so that the pumpkin is evenly distributed.
Season the mixture with chili powder, cumin, paprika, cayenne pepper (if using), salt, and pepper. Bring the chili to a simmer.
Once simmering, reduce the heat to low and cover the pot. Let it cook for 45 minutes to an hour, stirring occasionally, to allow the flavors to meld together.
Taste and adjust seasoning if necessary. If the chili is too thick, add more beef broth to reach your desired consistency.
Serve hot, garnished with shredded cheddar cheese and fresh cilantro if desired.