Preheat your oven to 350°F (175°C). Cook the pasta shells according to package instructions. Drain and set aside.
In a skillet over medium heat, cook the ground beef and onion until the meat is fully browned. Drain any excess fat.
Stir in taco seasoning, black beans (if using), and about ½ cup of salsa. Mix until fully combined. Remove from heat.
Spoon the beef mixture into each cooked pasta shell. Arrange the stuffed shells in a greased 9×13-inch baking dish.
Pour the remaining salsa over the shells, then sprinkle shredded cheddar and mozzarella cheese on top.
Cover with foil and bake for 20 minutes. Remove the foil and bake an additional 5–10 minutes, until the cheese is melted and slightly golden.
Garnish with fresh cilantro or green onions if desired. Serve hot.
Enjoy!