Place shrimp and marinade in a bowl, cover and chill at least one hour or overnight.
Preheat grill to medium-high heat. In a large bowl stir together ground beef, egg, soy sauce, garlic powder, salt and pepper until combined. Form into four patties and let sit at room temp for 15-30 minutes.
Lightly grease grill and add patties. Cook 4-5 minutes each side, or until until center reaches desired doneness and outsides have grill marks. Remove and lightly cover with foil to keep warm.
Meanwhile: Drain and discard liquid from shrimp. Grill 4-5 minutes, rotating midway, or until opaque and cooked through.
Toast buns if desired. Top each with burger patty, shrimp and avocado slices.