Heat a skillet over medium heat and add the ground meat. Cook until browned.
Stir in the chopped onions and cook until translucent.
Add the black beans and cooked rice, mixing well to combine.
Season with salt, pepper, and your choice of spices (cumin, chili powder).
Warm the tortillas in another skillet or microwave until soft.
Lay a tortilla flat and spoon the meat mixture down the center.
Top with shredded cheese, lettuce, tomatoes, and avocado.
Drizzle with salsa and add a dollop of sour cream if desired.
Fold in the sides of the tortilla, then roll it up tightly from the bottom.
Serve immediately, or wrap in foil for an on-the-go meal.