Take a chopping board, and finely chop the onions, capsicums, and carrots. Peel and cut the apples and potatoes into small half-inch chunks.
Boil water in a pot, add salt, and add the potatoes. Lower the flame to medium, and keep the lid open. Cook them for 5-8 minutes, and if the fork is being inserted into the potatoes easily, then they are done.
Sieve out the water from the potatoes, and let them rest at room temperature for 10-15 minutes.
Then, in a bowl, add the potatoes, apples, carrots, capsicum, onions, oregano, red chili flakes, and vinegar, and mix well.
Stir some mayonnaise in the salad till you get a smooth consistency, and add black pepper and salt.
After that, cover the bowl with plastic wrap, and store it in the fridge for 8 hours at least to settle the ingredients and let their flavors emerge.
While serving, sprinkle on some chopped onion, capsicum, carrot, and cilantro to add an extra bit of freshness.
Your Puerto Rican potato salad is ready.