Make the serrano mayo: Whisk together mayonnaise, serrano and lime juice in a medium bowl. Season with salt, and set aside.

Make the burritas: To a large nonstick skillet over medium-high heat, add bacon, and cook, stirring constantly, until golden, 2 to 3 minutes. Add onion, and cook, stirring, until light golden brown around the edges, 3 minutes. Add shrimp, and cook, tossing until they curl and are just cooked through, 2 minutes. Turn off the heat, stir in the lime juice and toss to combine. Season lightly with salt, and sprinkle cheese all over the shrimp. Cover the pan to melt the cheese.

Working with one tortilla at a time, lightly warm them in a large comal or a dry skillet over medium-low heat, turning often with tongs, 30 to 45 seconds per side. Transfer to a large piece of foil and repeat with the remaining tortillas.

Arrange tortillas on a clean work surface. Spread a tortilla with serrano mayonnaise, then top with a few slices of tomato, a sprinkle of lettuce and ½ to ⅔ cup of the shrimp filling. Fold the short sides of the tortilla over the filling; while keeping the sides folded, fold the bottom up and over the filling, then tightly roll. Set aside on a plate while you assemble the rest.

Wipe the skillet clean and heat over medium-high. Working in batches if needed, place the burritas seam-side down in the dry skillet, and cook, turning occasionally with tongs, until light golden brown on all sides, 2 to 5 minutes. Wrap burritas in foil and slice in half if desired, then serve immediately.