Wash tomatoes, cut on top like a washer lid and remove the inside.
Strain the tuna from the water which is in the can.
In a bowl, add tuna, the chopped onion, parsley, some olive oil and stir.
Fill the tomatoes and leave them for awhile in the fridge to freeze and serve.
Tips:
If you want, you can add 1-1.5 tbsp mayonnaise in the mixture for more flavour.
The inside of the tomatoes you can mash it and keep it in the freezer to cook a sauce.