1. Heat olive oil in a large skillet over medium-high heat. Add onion, garlic, salt, black pepper, and beef to pan; cook 5 minutes or until meat is browned and vegetables are tender, stirring occasionally to crumble beef.
2. Add carrot, chili powder, sugar, oregano, and red pepper; cook 2 minutes, stirring occasionally. Stir in tomatoes; bring to a boil. Reduce heat to medium; cook 10 minutes or until thickened and carrot is tender, stirring occasionally.
3. Partially mash 1 cup beans with a fork or potato masher. Add mashed beans and remaining whole beans to pan; cook 1 minute or until thoroughly heated. Spoon 1 cup bean mixture onto bottom half of each roll; top each serving with 1 red onion slice and top half of roll.