How to Make It
In a large skillet, heat 2 tablespoons of the olive oil. Add the shrimp, season with salt and pepper and cook over moderately high heat until barely cooked, about 2 minutes. Using a slotted spoon, transfer the shrimp to a medium heatproof bowl. Add the onion and red pepper to the skillet, cover and cook over moderate heat, stirring a few times, until softened, about 5 minutes. Transfer to the bowl. Heat the remaining 1 tablespoon of olive oil in the skillet. Add the garlic and cook until fragrant, about 1 minute. Add the cumin, turmeric and oregano and cook, stirring, for 30 seconds. Add the red wine vinegar and fish stock and boil over high heat until reduced to 1 cup, about 4 minutes. Stir in 1/2 teaspoon of salt until dissolved. Pour the marinade over the shrimp and vegetables in the bowl and stir well. Let cool to room temperature. Stir in the cilantro. Cover the shrimp and refrigerate for at least 6 hours or overnight.
In a medium saucepan, cover the potatoes with water and bring to a boil. Cook over moderately high heat until tender, about 8 minutes. Drain the potatoes and return them to the pan. Shake the pan over moderate heat to dry them out, about 10 seconds. Pass the potatoes through a ricer into a large bowl. Cover and refrigerate the potatoes until chilled.
Stir the vegetable oil, lime juice and ají amarillo paste into the chilled potatoes and season with salt and pepper.
Spread the potatoes on a rimmed platter in a 1-inch-thick layer and spread the mayonnaise on top. Arrange the avocado slices over the mayonnaise and season with salt. Spoon the marinated shrimp, vegetables and sauce over the avocado. Garnish with the cilantro leaves and serve.
Ají amarillo paste, made from yellow chiles, is available at specialty food stores and online at tienda.com.