Heat oil in a large pot over medium-high heat. Add ground beef, onion, bell pepper, and garlic, and cook 8 to 10 minutes, breaking up beef into small crumbles and stirring occasionally.
Add tomato paste, chili powder, cinnamon, salt, and pepper, and cook, stirring frequently, 2 minutes.
Stir in tomatoes, pumpkin, and water, and bring to a boil over high heat.
Reduce heat, and simmer 30 minutes, stirring occasionally.