Tuna salad is made a lots of variety as you can add more ingredients than celery, but this is my favorite combination with lemon. First drain the tuna can, try to remove the oil. If you use tuna in salted water later on just add some drop of olive oil othervise the salad will be dry. So the oil is important ingredient but only in small amout. Than flavor the tuna with salt and pepper, the mayonnaise and add the sliced celery and lemon. Add 4-5 drop of lemon juice also. Stir it and before serving add the teared rucola as well. Half two rolls and fill with tuna salad. You may garnish the plate with more rucola and lemon slices.