To make the mayonnaise: Combine the mayonnaise with the lime zest in a small bowl. Season with salt and pepper to taste, mix well, and set aside.

To make the tostada filling: Season the shrimp and scallops with the salt and pepper. Heat

1 tablespoon of the butter with 1 tablespoon of the oil in a large skillet over high heat. Once the butter has begun to foam, add the shrimp. Cook for 1 or 2 minutes per side, just until nicely seared and browned on the outside and just cooked through. Scrape into a bowl. Return the skillet to the heat, add the remaining 1 tablespoon each butter and oil, and heat until the butter foams. Add the scallops and cook for a minute per side, or until the tops and bottoms are browned and the centers are no longer translucent; they should be medium-rare. Remove from the heat. As soon as you can handle them, slice the scal­lops thin and set aside.

To build the tostadas: Spread about a table­spoon of mayo on each tostada, top with a layer of scallops, a couple of tablespoons of salsa, and a layer of shrimp. Finish with some avocado slices and add hot sauce to taste. Serve immediately, passing the remaining salsa at the table.