Chop the apples, celery, and onions into small pieces. Place in a medium sized bowl.
Add the tuna and mayonnaise to the same bowl and mix thoroughly. Refrigerate until ready to use.
Tostones
Heat coconut oil in a skillet on medium.
Peel the plantains. Slice each plantain into 3 chunks. Cut each chunk in half lengthwise.
Fry each chunk of plantain, about 2 -3 minutes per side, or until a light golden brown. They should NOT be cooked all the way through.
Remove plantains from frying pan. One at a time, place each chunk between two pieces of parchment paper. Using a plate or something flat, press down and flatten the plantain.
Place the flattened plantains back into the frying pan, and cook both sides for 2-3 minutes until they are crispy and golden.
Tuna Melt Tostones
Pre-heat the broiler on the oven. Place the rack on the top position.
Place the tostones onto a baking sheet. Spoon the tuna salad onto each tostone. If using cheese, place it on now.
Place the baking sheet under the broiler, and broil for only about 45 seconds. You want the salad heated and the cheese melted if you're using it.
When finished, top with any remaining optional toppings, and serve!