Heat olive oil in a large skillet over medium heat and cook the diced onions and bell peppers for 5 to 6 minutes until softened and starting to turn golden at the edges.

Add the garlic and cook for 1 more minute until fragrant.

Transfer the vegetables to a 6-quart slow cooker and add the black beans, pinto beans, kidney beans, diced tomatoes, chili powder, cumin, smoked paprika, minced chipotle, adobo sauce and vegetable broth.

Stir well, then cover and cook on low for 4 to 5 hours, or on high for 2 to 3 hours, until the peppers are completely tender and the chili smells deeply smoky.

Uncover and mash about 1 cup of the beans against the side of the slow cooker with a spoon, then stir back in; this thickens the chili without any extra flour or starch.

Season with salt and black pepper, tasting as you go since the canned beans carry their own sodium.

Switch to the warm setting and let the chili sit uncovered for 10 minutes to settle before guests start serving themselves.