In a small bowl, mix together the chili powder, cumin, garlic powder, salt, and pepper. Add the shrimp to a zip top bag (recommended) or a medium bowl. Add the spice mixture to the shrimp and toss until they are completely coated.
Heat a large pan or skillet over medium-high heat. Add the oil and the shrimp to the skillet. Cook the shrimp for 2-3 minutes on each side, until the outside is slightly browned and the shrimp is cooked through.
While the shrimp is cooking, prepare the dressing. In a small bowl, whisk together the Greek yogurt, lime juice, mayonnaise, cilantro, garlic, cumin, salt, and pepper. Set aside.
Warm the tortillas in the microwave for 10-20 seconds, until they are soft and pliable.
Assemble the tacos by placing ¼ cup of the sliced red cabbage, the diced avocado, and 5-6 shrimp. Drizzle with the dressing and top with extra freshly chopped cilantro.
Serve with lime wedges on the side and enjoy your delicious shrimp tacos with homemade dressing!