Scoop out meat from each avocado half, and cube. Reserve the peels. Place cubes in a bowl. Sprinkle cubes and inside of peels with lemon juice.
In the bowl with avocado, gently mix the shrimp, peas, olives, onion, and celery. Season with garlic powder, onion powder, salt and pepper. Fold in enough mayonnaise to evenly moisten all ingredients. Spoon the mixture into the reserved peels, and serve within 1 hour.