01 - Preheat oven to 400°F and line a baking sheet with parchment paper.
02 - In a skillet over medium heat, sauté diced onion until translucent, about 3 minutes. Add ground beef, garlic powder, salt, and black pepper. Cook until beef is browned, breaking apart as it cooks. Drain excess fat.
03 - Mix in ketchup, yellow mustard, Worcestershire sauce, and pickles to the cooked beef. Stir well, then remove from heat and allow mixture to cool slightly.
04 - Flatten each biscuit round. Spoon 1 tablespoon beef mixture and 1/2 tablespoon shredded cheddar onto the center of each. Add a cube of mozzarella cheese.
05 - Fold dough over the fillings, pinching edges together to enclose and shape into a sealed ball. Position seam-side down on the prepared baking sheet.
06 - Brush each dough ball with beaten egg and sprinkle with sesame seeds.
07 - Bake on the center rack for 15–18 minutes, or until golden brown.
08 - Let cool for several minutes before serving. Accompany with your preferred burger dipping sauces.