In a medium bowl, combine tuna with greek yogurt and lemon juice. Mix until well combined. Add the celery, dill, cranberries and green onions and stir. Season with salt and pepper.
Cut avocado in half and remove pit. Fill avocado halves with large scoop of tuna mixture.
Using a paring knife, remove stem and core of heirloom tomatoes. Fill with large scoop of tuna mixture.
Recipe by Good Thyme Kitchen at https://www.goodthymekitchen.com/tuna-salad-cranberries-dill/