In a large skillet, cook the ground beef and chopped onion over medium-high heat until browned. Drain excess grease. Stir in ketchup, mustard, and chopped pickles. Season with salt and pepper and cool slightly.

Preheat oven to 375°F (190°C). Unroll crescent dough into four rectangles on a lightly floured surface, pressing perforations to seal.

Spread the beef mixture over the dough rectangles. Sprinkle evenly with shredded cheddar cheese. Roll each rectangle up tightly into a log, starting from a long side.

Slice each log into 6 rollups (24 total). Place on a parchment-lined baking sheet. Brush with egg wash and sprinkle with sesame seeds.

Bake for 12-15 minutes, or until golden brown and puffed.