Heat olive oil in a large pot over medium heat.
Add diced onions and sauté until translucent, about 5 minutes.
Stir in minced garlic and diced bell pepper; cook for another 2-3 minutes.
Sprinkle in cumin and chili powder, mixing well for about 1 minute.
Pour in the canned pumpkin puree, followed by the black beans and diced tomatoes.
Stir in the vegetable broth, bringing the mixture to a gentle simmer.
Season with salt and pepper, tasting to adjust as needed.
Let the chili simmer for at least 20-30 minutes, stirring occasionally.
Serve hot, garnishing with fresh cilantro.