Cook pearled couscous according to the package. Once cooked, rinse under cold water. This will prevent the couscous from sticking together as it cools. Drain well and place couscous in a mixing bowl. Add 1 tablespoon olive oil and mix well.
While pearled couscous is cooking, add all lemon vinaigrette dressing ingredients to a bowl. Mix well to combine and set aside.
Add castelvetrano olives, shallots, flat leafed parsley, dill, and tuna to the bowl and mix well to combine. Add dressing and fold the mixture with a spoon. Place in refrigerator for 1 hour to allow flavors to meld.