How to Make It
In a food processor, puree the tomatillos with the onion, serrano, garlic and cilantro. Scoop the avocado into the food processor, add the lime juice and puree. Season with salt and transfer to a serving bowl.
In a large skillet, heat the olive oil until shimmering. Add the onion and garlic and cook over moderate heat, stirring, until lightly golden, about 3 minutes. Add the jalapeños and cook until softened, about 1 minute. Add the shrimp, salt and pepper and cook, stirring occasionally, until the shrimp are just cooked through, about 3 minutes. Remove from heat and stir in the mayonnaise.
Serve the shrimp with tortillas, tomatoes, lime wedges,cilantro leaves and the avocado-tomatillo sauce.