We pour in about an inch of oil into the pan. When the oil is hot, we add the plantain pieces, lower the heat to medium-low, and cook for 3 minutes on each side. We want the plantains to be fork-tender but not too browned.
We remove the tender pieces one at a time from the pan with a fork, and place into the tostonera. We flatten and then place on a paper-towel lined plate while we continue with the rest of the plantains.
When all the pieces are flattened and the oil is hot again, we raise the heat to medium-high and add the plantains back to the pan. We cook for 2 minutes, turn, and then cook for another 2 minutes. We want them browned and crispy. We remove the pieces to the paper-towel lined plate and sprinkle with kosher salt.
We serve immediately with the mojo.