In a large skillet over medium-high heat, add the ground beef, chopped onions, and minced garlic. Cook until the beef is browned and the onions are softened, about 6-8 minutes. Drain any excess fat.

Stir in the ketchup, mustard, salt, and pepper. Mix well to combine and allow the mixture to cool slightly.

Lay out an egg roll wrapper on a clean surface with one of the corners facing you. Place about two tablespoons of the beef mixture in the center, adding a sprinkle of cheddar cheese on top.

Fold the corner closest to you over the filling, then fold in the two side corners, and roll it tightly toward the far corner. Seal the edge with a bit of water to ensure it stays closed.

In a large skillet, heat oil over medium heat. Fry the rolls in batches until they are golden and crisp all around, about 4-5 minutes per side. Remove and drain on paper towels.

Pair the egg rolls with your favorite dipping sauce, and enjoy!