For Creamy Avocado Sauce, add all ingredients to a food processor or blender. Blend till they combine well.
Preheat grill to medium heat. Place burgers on the grill and cook about 5 minutes on each side, flipping once (cooking time may vary) Alternatively, cook in the oven, microwave or in a skillet according to package directions).
Warm up the burger buns on the grill (or skillet).
Assemble burgers: Put a spoon of creamy avocado sauce on the bottom bun. Top with lettuce, onion and tomato. Then place the burger patty and top again with a dollop of the avocado sauce. Finish by placing the top bun and enjoy!