Heat the oil in a large skillet over medium heat. Add in the corn and onion, and cook for around 4 minutes, or until the onion is fragrant and transparent. Mix in the garlic, chili powder and cumin, and cook for another minute.
Add in the beans, rice and salsa. Cook for around 4 minutes, or until warm.
Serve over the lettuce. Sprinkle some cheese over top.