In a small mixing bowl, combine crabmeat, mayonnaise, celery and lemon juice. Add salt and pepper to taste. Chill for 30 minutes or up to two hours [you can do this step ahead of time].
Arrange crackers on a cutting board, plate or serving platter. Spread a thin layer of mashed avocado on each cracker. Top with about half a tablespoon of crab salad, a piece of cherry tomato. Garnish with chives, salt and pepper, as desired.
Recipe by In Good Taste at https://ingoodtaste.kitchen/diy-crostini-bar/