In a medium bowl, combine shrimp, taco seasoning mix, and 2 tablespoons fresh lime juice. Mix to coat.
Thread shrimp onto skewers, leaving about 1 centimeter of space between each shrimp. Note: if using bamboo skewers, soak them in water for 10 minutes to prevent burning.
Heat a grill on medium heat. Place skewers on grill and cook until shrimp are pink and slightly charred, about 1 minute per side. Remove shrimp from grill.
Optional: warm tortillas briefly on grill or in microwave.
Assemble tacos: carefully remove shrimp from skewers. Place 3-4 shrimp per tortilla. Top shrimp with a small handful of shredded lettuce, a sprinkle of diced onion, and salsa (to taste)