In a large saucepan or a Dutch oven, heat 1 tbsp. oil over medium. Add the garlic and most of the onion (save a small handful for garnish). Cook, stirring often, until the onion starts to soften, about 3 minutes. Add the bell pepper; cook, stirring often, until the pepper starts to soften, about 2 minutes more. Add the chili powder; cook, stirring until aromatic, about 30 seconds.
Add the tomatoes, chipotle and adobo sauce. Cover; simmer, stirring often, until the tomatoes are tender, about 6 minutes. Stir in the corn; simmer 5 minutes. Add the chicken and beans; cook, stirring often, until the chicken is cooked through, 5 to 10 minutes. Season with salt and pepper. Top with the basil and reserved onion.