In a large mixing bowl, whisk together the olive oil, lime juice, lime zest, chili powder, cumin, garlic powder, and salt. Add the shrimp to the bowl and toss until every piece is thoroughly coated. Cover and refrigerate for 15 to 20 minutes to allow the flavors to penetrate the seafood.
Preheat your outdoor grill or an indoor grill pan to medium-high heat. Ensure the grates are clean and lightly oiled to prevent the shrimp from sticking. If you are using wooden skewers, make sure they have been soaked in water for at least 30 minutes beforehand.
Thread the marinated shrimp onto skewers or place them directly on the grill grates. Cook for 2 to 3 minutes per side. You will know they are done when they turn opaque and form a light pink, C-shaped curve. Be careful not to overcook them, as they can become rubbery.
While the shrimp are resting, place your tortillas on the grill for about 30 seconds per side. This makes them pliable and adds a nice charred flavor. Alternatively, you can wrap them in a damp paper towel and microwave them for 20 seconds.
To build your tacos, start with a warm tortilla. Layer a small handful of cabbage slaw in the center, followed by 3 or 4 grilled shrimp. Top with avocado slices, a dollop of sour cream, and a sprinkle of fresh cilantro. Serve immediately with extra lime wedges on the side.