Drain the tuna and add to a large bowl along with the mayo, chopped avocado, chopped dill pickle and lemon juice.
2 cans chunk or flaked tuna packed in water, 1 dill pickle,, 2 tablespoon mayonnaise, ½ small avocado, cut into chunks, 1 teaspoon lemon juice
Mix everything together with a fork, mashing the avocado as you mix, until well combined. Taste and add salt and pepper as needed.
Place oven rack in the top third of oven (2nd rack from the top). Preheat broiler to high.
Slice the tomatoes into 6 thick slices. Place on a foil or parchment lined tray. If your broiler tends to get very hot use foil instead of parchment paper.
Scoop tuna onto tomato slices and top with grated cheese.
Broil for 2 to 3 minutes or until cheese is melted and bubbling. Remove from oven, top with fresh parsley and serve.