Peel and very finely slice red onion (you can also use a mandoline) and soak in cold water for at least 1 hour or overnight in the refrigerator. Make sure all onions are submerged in the water. Then drain well or spin dry to ensure most water is gone and doesn't water down your salsa later.
Add sliced onions, ají, chopped cilantro, juice of lime, and salt to a large bowl and mix well with your hands. Set aside.
To make Tacu Tacu
Heat the oil in a pan, add and cook the onion, garlic, aji Amarillo, and oregano.
Add and stir the beans, mashing them with a wooden spoon, or even better, with a potato masher. Season with salt and pepper.
Add the rice and continue stirring and mashing until the mixture is thick like a paste.
Divide into four portions, fry every one and try to form a log moving the pan back and forth with a firm but light movement. The outside of the tacu tacu must be slightly crispy while the inside remains mushy.
Serve with Salsa Criolla, plantains, and fried egg.
