10-12 oz. canned tuna
1/4 cup mayo
1 tsp. Dijon mustard
1 T lemon juice
1/4 tsp. celery seed
1/2 cup finely chopped celery
1 T capers, chopped
2 green onions, thinly sliced
Drain tuna into a fine-mesh strainer and press down to drain out the oil (or water if you use water-packed tuna.) While tuna drains stir together the mayo, Dijon, lemon juice and celery seed
Chop the celery and capers and thinly slice the green onions.
When the tuna has drained, put it in a bowl (with a snap-tight lid if you won't be eating it all at once.) Stir in the dressing until it's well-distributed in the tuna, then mix in the celery, capers, and green onions.
This kept well in the fridge for several days.