In a bowl, combine shrimp, olive oil, chili powder, cumin, garlic powder, lime zest, lime juice, salt, and pepper. Toss until the shrimp are evenly coated with the seasoning mixture.
Preheat a grill or skillet over medium-high heat. Once hot, add the marinated shrimp in a single layer. Cook for 2-3 minutes on one side until just opaque, then flip and cook for an additional 1-2 minutes. Remove from heat.
While the shrimp are cooking, warm the corn tortillas briefly on the grill or in a dry skillet until soft and pliable.
To assemble the tacos, place a layer of shredded cabbage on each tortilla, followed by a few shrimp, avocado slices, and a sprinkle of fresh cilantro.
Add a dollop of sour cream or Greek yogurt if desired and a squeeze more of lime juice for extra zing.