In a large skillet, cook ground beef over medium-high heat until no pink remains, about 10 minutes. Drain any fat, crumble and return meat to skillet.
Add onion, ancho chili powder and cumin. Cook, stirring often, until onions are slightly softened, about 5 minutes.
Stir in beans and salsa. Cook until heated through, about 5 minutes. Stir in corn (do not need to thaw) and rice until well combined.
Spoon about 1 cup (250 ml) of the rice mixture in the center of each tortilla. Top with 1/2 cup (125 ml) lettuce and 1/4 cup (50 ml) cheese and two pieces of avocado. Add a sprig of cilantro, a squeeze of lime and dollop of sour cream/yogurt if desired. Fold bottom edge, then sides; roll up.
Rice and beef burritos can be served cold, at room temperature or warmed in the microwave if desired.