Heat oil in a large skillet over medium-high heat. Add ground beef and cook, breaking it up, until browned, about 5-7 minutes. Drain excess fat.
Add onion and garlic to the skillet; cook until softened, about 2 minutes.
Stir in taco seasoning and water. Bring to a simmer and cook until thickened, about 3-4 minutes.
Add black beans and stir until heated through, about 1 minute. Remove from heat.
For tacos: Warm tortillas. Fill each with beef mixture and top with cheese and desired toppings. For burritos: Place a large tortilla on a flat surface. Spoon beef mixture down the center, top with cheese and other fillings. Fold in sides and roll tightly.
Serve immediately.
Tips
For a lighter version, use ground turkey or chicken.
Leftover filling can be stored in the fridge for up to 3 days and reheated.
Customize with your favorite taco toppings like pickled jalapeños or hot sauce.