In a mixing bowl, stir together the Greek yogurt, lemon juice, Dijon mustard, salt and pepper, until well combined. Add tuna and celery, and stir until well combined.
Place the lettuce into meal prep containers. Divide the tuna on top of the lettuce. Add the mini pita bread, bell peppers and grapes to the containers.
Video
Notes
Storage: The tuna salad will keep well in the fridge for 3 to 4 days.