In a skillet, heat olive oil over medium heat and sauté the chopped onion until softened, about 5 minutes.
Add garlic and cook for an additional 1 minute until fragrant, but be careful not to overcook the garlic.
Add the bell peppers and cook for another 2-3 minutes.
Transfer the sautéed vegetables to the slow cooker.
Add the canned tomatoes, beans, chili powder, smoked paprika, cumin, salt, and pepper to the slow cooker.
Add vegetable broth to the slow cooker (start with 2 cups). If you prefer a thicker consistency, feel free to reduce the amount of broth or allow it to cook uncovered to reduce the liquid.
Stir everything to combine.
Cover the slow cooker and set it on low for 6-8 hours or on high for 3-4 hours.
Once the chili is done, stir and taste. Adjust the seasoning if needed.
Serve warm with toppings like shredded cheese, sour cream, cilantro, or avocado if desired.