Open the tuna and drain water or oil.
Chop the onion, celery, and scallions.
Arrange the tuna in a mixing bowl. Add mayonnaise, chopped onion, celery, and scallions.
Add Parmesan cheese and garlic powder. Mix well
Slice the Croissant in half and then lay a piece of lettuce flat on one slice of the bread. Scoop some tuna salad over the lettuce. Top with the other bread slice.
Serve and Enjoy!