Heat the olive oil in a skillet over medium heat. Add the diced onion and bell pepper, cooking until softened. Stir in the minced garlic and cook for another minute until fragrant.
Transfer the cooked vegetables to the slow cooker. Add the pumpkin puree, black beans, kidney beans, diced tomatoes, vegetable broth, tomato paste, chili powder, cumin, smoked paprika, oregano, cayenne pepper, salt, black pepper, and maple syrup.
Stir everything together until well combined, making sure the tomato paste is fully incorporated into the mixture.
Cover and cook on Low for 6 hours or on High for 3 to 4 hours, allowing the flavors to develop and the chili to thicken naturally.
Just before serving, stir in the fresh lime juice and taste for seasoning. Adjust with additional salt or chili powder if desired.
Ladle the chili into bowls and finish with your favorite toppings such as shredded cheddar cheese, sour cream, avocado, cilantro, green onions, or crushed tortilla chips.