In a blender or food processor, add shrimp and pulse until coarsely chopped. Remove shrimp to a bowl and stir in red onion, egg, and Old Bay seasoning. Form into patties and put in refrigerator for 15 minutes while preparing the rest.
Mix vinegar and fat-free mayo until well blended. Heat either a grill or a non-stick skillet and spray with cooking spray. Add shrimp burger patty to heat and cook for about 5 minutes per side.
Lightly top shrimp burger with fat-free mayo mixture. Serve with avocado and red onions for toppings.
Notes
*Serving sizes on the recipes are not necessarily "bariatric sized" portions but are "traditional" portion sizes.