In a large pot over medium heat, warm the oil. Add the onion and bell pepper. Cook, stirring occasionally until the onion and pepper are soft, about 8 minutes. Add the tomatoes and mix. Add the chili powder, cumin, brown sugar, salt, and cayenne. Mix well. Bring to a simmer. Add the broth and all of the beans. Bring to a simmer and cook at a low simmer for about 30 to 40 minutes until thickened. Taste and adjust salt if needed. Serve garnished with toasted pumpkin seeds.