In a large heavy pot, add enough vegetable oil to cover the entire plantains and heat the oil over medium high heat.
Add the plantains to the heated oil. Fry for about 10 to 15 minutes per side. Carefully remove the plantains with a slotted spoon, and place them on a plate lined with paper towels to absorb excess oil.
Let the plantains cool for 3 minutes. Then, place the plantains on a piece of plastic wrap and cover with another piece of plastic wrap. With a flat pot cover, press well the plantains, flattening them about to ¼” thickness.
Dip each slice in salted water. Then using tongs add them back in the hot oil in a single layer (need to work in batches) and fry for an additional 3 minutes on each side. Be careful when you fry the soaked plantains, as droplets of water will cause the oil to splatter.
Remove the tostadas with slotted spoon and transfer them to a plate lined with paper towels to absorb oil, sprinkle with salt, to taste, transfer to a serving plate and serve hot with guacamole, hogaoand aji on the side.