Cook the elbow macaroni according to package directions. Drain and allow to cool completely.
In a large bowl, combine the boiled shrimp, cooked macaroni, chopped hard-boiled eggs, chopped onion, mayonnaise, and garlic powder.
Season with salt and black pepper to taste.
Mix until everything is evenly coated.
Arrange the lettuce leaves on a serving platter or individual plates.
Spoon the shrimp salad onto the lettuce leaves.
Garnish with tomato wedges and serve chilled.