Heat the slow cooker and add a splash of olive oil. Sauté the diced onion until it becomes translucent and fragrant, about 3-4 minutes.
Add the minced garlic to the onion and cook for another minute, until fragrant and slightly golden.
Stir in the pumpkin puree, vegetable broth, chili powder, cumin, cayenne pepper, and a pinch of salt and pepper, mixing well to combine and dissolve the spices.
Drain and rinse the black beans, then add them to the slow cooker mixture, stirring to distribute evenly.
Cover the slow cooker and set it to low. Let the chili simmer for about 4 hours, allowing flavors to meld and the chili to thicken. During cooking, you can gently stir once or twice if needed.
Once cooked, taste and adjust seasoning with more salt, pepper, or spices as desired.
Serve the pumpkin chili hot, garnished with your favorite toppings like chopped cilantro, sour cream, or shredded cheese if desired. Enjoy the rich, velvety texture and flavorful, spicy aroma.