Heat olive oil in a large pot or Dutch oven over medium heat until shimmering. Add the diced onion and cook for 4-5 minutes until translucent.
Add the bell peppers and jalapeño (if using) to the pot and cook for another 3-4 minutes until they begin to soften.
Stir in the minced garlic and cook until fragrant, about 30 seconds, being careful not to burn it.
Add all the spices (chili powder, cumin, smoked paprika, oregano, and cinnamon) and stir constantly for 1 minute to toast the spices and release their flavors.
Pour in the vegetable broth and use a wooden spoon to scrape up any browned bits from the bottom of the pot – these contain tons of flavor!
Add the pumpkin puree and stir until completely incorporated into the liquid. The mixture should start to thicken nicely.
Add the diced tomatoes with their juices, all three types of beans, and maple syrup or brown sugar. Stir well to combine everything.
Bring the chili to a simmer, then reduce heat to medium-low. Cover partially with a lid and cook for 20-25 minutes, stirring occasionally to prevent sticking.
Stir in the lime juice and season with salt and pepper to taste. The acidity of the lime helps balance the sweetness of the pumpkin.
Let the chili rest for about 5 minutes before serving. This allows the flavors to meld together and the chili to thicken slightly.
Serve hot in bowls with your choice of toppings. A sprinkle of toasted pumpkin seeds adds a delightful crunch and ties in the pumpkin theme!