Combine the tequila, lime zest, lime juice, garlic, cilantro, red pepper flakes, red onion and olive oil in a zipper sealable plastic bag or a mixing bowl. Add the shrimp and mix together to coat all the shrimp in the marinade. Refrigerate and marinate for 30 minutes to as long as 4 hours.

Pre-heat an electric griddle to 400˚F or pre-heat a large skillet over medium-high heat.

Remove the shrimp and onions from the marinade and toss onto the griddle or into the skillet. Season with salt and cook quickly over high heat, tossing or turning several times for 3 to 5 minutes, until cooked through but not overcooked.

Remove the shrimp and onions to a side plate. Wipe the griddle or skillet clean and warm the tortillas on the griddle or in the skillet. Fill the warm tortilla with some shrimp and onions, some shredded lettuce and some salsa and serve with lime wedges and fresh cilantro leaves if desired.