Ecuadorian Shrimp Ceviche

Name: Ecuadorian Shrimp Ceviche
Ingredients: 1/2 small red onion, halved and sliced paper thin; 1 fresno, jalapeño or other small chile, sliced paper thin (optional); 3/4 cup fresh lemon juice (from about 6 lemons); 2 pounds 31/40 count shrimp, peeled and deveined, including tails, (shells or tails reserved); 1/4 cup ketchup; 1 cup fresh orange juice (from about 3 oranges); 2 teaspoons salt, plus more to taste; 3 tablespoons finely minced fresh cilantro; 2 green plantains, peeled; Vegetable oil for frying