Start by heating one frying pan to medium heat, filled with an inch of oil. Heat an additional frying pan to high heat coated with a small amount of oil. This pan will be used for the steak. Cut the ends of the green plantain and slice along the side to remove the outside peel. Trim the plantain into 4 halves and place them in the pan with the inch of oil when it is ready. Slice the skirt steak in half in about 6 inches in length and place both side by side in the other frying pan.
The steak will take 3-4 minutes each side depending on the desired degree of doneness. While the plantains fry, prepare your veggies (red onion, tomato, and romaine lettuce) by cutting them so they are ready to be placed in the tostone sandwich. *Keep an eye on the plantains and make sure they don’t burn!
Remove the plantains from the frying pan when they are golden yellow. Do not turn off the heat because you will have to fry these once more. You will have to flatten the golden plantains with a tostonera or a chopping board until they are as big as your palm. After flattening, place them back into the frying pan. This should take about 2-3 minutes each side or until a golden-brown color. Place them on a paper towel covered plate to drain the excess oil.
Let them cool and drain for about 2 minutes and then start creating your sandwich. Mix the mayonnaise, ketchup, and ground garlic together. Just like a regular sandwich, apply mayo-ketchup-garlic sauce on the plantains – place your choice of meat – 2 thin slices of tomato – thin cuts of red onion – 2 small romaine lettuce leaves. Sprinkle salt for taste, enjoy!