Stir in the minced garlic and diced zucchini, cooking for another 2-3 minutes until the zucchini begins to soften and the garlic is fragrant.
Add the black beans, kidney beans, diced tomatoes (with juice), tomato sauce, vegetable broth, chili powder, cumin, smoked paprika, salt, and black pepper. Stir well to combine all the ingredients.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 25-30 minutes, stirring occasionally, until the flavors meld and the chili thickens slightly.
Taste the chili and adjust seasoning with additional salt, pepper, or chili powder if desired. If the chili is too thick, add a splash of vegetable broth; if too thin, simmer uncovered for a few more minutes.
Serve hot in bowls, garnished with chopped cilantro, a dollop of sour cream, or shredded cheese if desired. Enjoy your hearty vegetarian chili with crusty bread or tortilla chips!