Heat olive oil in a large skillet over medium heat. Add chopped onion and minced garlic. Sauté for 2-3 minutes, until fragrant and soft.

Add the ground beef. Cook, breaking up the meat with a spoon, until browned and cooked through, about 6-7 minutes.

Stir in ground cumin, chili powder, salt, and black pepper. Mix well, then add black beans and cook for another 2 minutes to heat through. Remove from heat.

Warm the flour tortillas in a skillet or microwave for about 15 seconds, until pliable.

Lay each tortilla flat and spoon 60 grams of cooked rice onto the center. Add 1/4 of the beef and bean mixture. Top each with shredded cheese, diced tomatoes, and chopped lettuce.

Add salsa and a spoonful of sour cream, if desired.

Fold in the sides of the tortilla and roll up tightly from the bottom to seal the burrito.

Serve immediately, or toast the burritos in a dry skillet for 2 minutes per side for a crispy exterior.