1. Heat oil in a large nonstick skillet over medium heat. Add onion and cook, stirring, until the onion begins to brown, about 5 minutes. Coarsely chop 1 tomato. Add it to the pan along with rice, beans, chili powder, and salt. Cook, stirring frequently, until the tomato cooks down, about 5 minutes. Let cool slightly.
2. Coarsely chop the remaining 1 tomato. Combine with cilantro, lime juice, salsa bean mixture and cheese in a medium bowl.
3. Top lettuce with the bean mixture. Serve sprinkled with tortilla chips and lime wedges.