In a small mixing bowl, blend the mayonnaise, sour cream, lime juice, garlic powder, and Sriracha until smooth; set aside to allow flavors to meld. For ease of use, you may transfer the sauce to a squeeze bottle.
Shred the cabbage finely, dice the avocado and red onion, and chop the cilantro coarsely. Arrange each topping in separate serving dishes for convenience.
Place the shrimp in a medium bowl after patting dry with paper towels. Sprinkle with sea salt, black pepper, cayenne, cumin, and minced garlic. Stir until the shrimp are well-coated with seasoning.
Heat a large non-stick skillet over medium-high heat. Pour in the olive oil, then arrange the shrimp in a single layer. Sauté for 1 to 2 minutes per side until they turn opaque and slightly pink. Transfer the cooked shrimp to a platter and let cool slightly.
Warm tortillas individually over an open gas flame, on a hot griddle, or in a dry skillet until lightly charred or golden, about 10–30 seconds per side depending on method.
Assemble the tacos by placing shrimp and toppings onto each toasted tortilla. Finish with a generous drizzle of the garlic-lime crema and serve with a lime wedge on the side.