Prepare the Prik Nam Pla (Chili Fish Sauce): In a small bowl, combine the sliced red chili pepper, 3 tablespoons of fish sauce, and the juice from 1 lime wedge. Set aside.
Heat the cooking oil in a wok or large skillet over medium-high heat. Add the minced garlic and stir-fry until fragrant, about 10 seconds.
Push the garlic to the side and pour in the beaten eggs. Scramble quickly until they are about 80% cooked.
Add the cold cooked rice to the wok. Break up any clumps with a spatula and toss to combine with the eggs and garlic.
Season with 1 tablespoon soy sauce, 1 tablespoon fish sauce, and a pinch of sugar. Stir-fry on high heat for 2-3 minutes until the rice is hot and evenly coated.
Gently fold in the lump crab meat and chopped scallions. Cook for another 60 seconds, tossing gently to heat the crab without breaking the lumps.
Remove from heat immediately. Garnish with cucumber slices, a sprig of cilantro, and a lime wedge. Serve hot with the prepared Prik Nam Pla sauce on the side.