Classic U.S.A. Tuna Salad

1/3 cup mayonnaise
1 small onion, minced
1 tsp white vinegar
1/2 tsp salt
1/4 tsp pepper
1 can tuna, drained and flaked
2 hard boiled eggs, chopped coarse
1 cup thinly sliced or chopped celery
Mix all ingredients, serve over greens, garnish with deviled egg halves or stuffed olives.