Bring a pot of lightly salted water to boil. Add pasta and cook until al dente, about 8 to 10 minutes. Drain and set aside.
In a large bowl, whisk together lemon juice, mustard and mayonnaise. Season with salt and pepper to taste. Slowly whisk in olive oil. Add tuna, separating into thick chunks. Add capers and stir to combine. Pour pasta into tuna mixture and stir gently to combine. Cover and refrigerate.