First, wash the cherry tomatoes under cool water and pat them completely dry. Using a small, sharp knife, carefully slice a thin layer off the top of each tomato. Then, use a small spoon or a melon baller to gently scoop out the seeds and pulp, creating a hollow little cup. Be careful not to puncture the sides.
In a medium-sized bowl, add the drained tuna. Use a fork to flake it into fine pieces. Next, add the mayonnaise, Dijon mustard, fresh lemon juice, and chopped parsley. Mix everything together until it is well combined and has a creamy, consistent texture. Season with salt and pepper to your liking.
Now it's time to stuff your tomatoes. Using a small spoon or a piping bag for a cleaner look, carefully fill each hollowed-out cherry tomato with the tuna salad mixture. You can fill them generously, letting the mixture mound slightly over the top for a more abundant appearance. Arrange the filled tomatoes on your serving platter.
For a final touch, you can garnish the stuffed tomatoes. A sprinkle of extra chopped parsley, a single caper on top of each, or a small piece of an olive adds visual appeal and an extra layer of flavor. Serve them immediately, or cover and chill them in the refrigerator for about 30 minutes before serving for a more refreshing taste.