In a skillet over medium heat, cook the ground beef until browned. Drain excess fat, if desired.

Stir in the chopped onion, ketchup, mustard, salt, and pepper. Cook for another minute until everything is heated through and mixed well.

Remove the skillet from heat and fold in the shredded cheddar cheese, allowing it to melt slightly.

Lay an egg roll wrapper on a flat surface with one corner facing you. Spoon about 2 tablespoons of the beef mixture onto the center of the wrapper. Fold the bottom corner over the filling, then fold in the sides and roll it tightly toward the top corner. Seal the edge with a little water.

Heat oil in a deep frying pan over medium-high heat. Carefully add the egg rolls, frying them for about 3-4 minutes on each side until golden brown and crispy. Remove them and let them drain on paper towels.

Serve hot with your favorite dipping sauces!