Put the onions, jalapenos and lemon juice in a large bowl and leave to one side to marinate.
Peel and devein Ecuadorian white shrimp and place the shells and tails to one side.
Boil a medium-sized pot of water and add the shrimp. Cook for only about 3 minutes.
Once cooked place the shrimp straight into an ice bath.
Add the shells and tails to the water, turn off the heat, and allow to stew.
Drain and dry the Ecuadorian white shrimp. Mix with the onions, jalapenos and lemon juice and marinate for about 15 minutes in the fridge. Leave the shrimp shells to soak.
Strain out the shells and add 3 cups of the poaching liquid to the shrimp, along with the ketchup, orange juice, salt, cilantro and stir until thoroughly combined.
Cover and allow to chill in the refrigerator for 1 hour, but overnight is best.
Heat about 1 inch of oil in a heavy-bottomed pan or a deep fryer to 375 degrees.
Grate the plantains into large slices. Fry them until golden brown and crisp. Place on paper towels to absorb excess oil. Sprinkle with salt, then repeat with the remaining plantains.
To serve, add the ceviche into serving bowls, and include plenty of liquid. Sprinkle with fried plantains and serve ice cold, with the remaining plantains on the side.