Pat the fish dry with paper towels. Combine chili powder, smoked paprika, garlic powder, and salt in a small bowl. Sprinkle evenly on both sides of the fish, pressing gently to adhere.
Heat olive oil in a nonstick skillet over medium heat. Place the fish in the skillet and cook until it flakes easily with a fork and reaches an internal temperature of 145°F, roughly 4-7 minutes per side. Remove from heat and let rest.
In a small bowl, whisk together Greek yogurt, lime juice, garlic powder, sriracha, and salt. Add water, 1 teaspoon at a time, until the sauce reaches your desired consistency.
Heat tortillas one at a time in a dry skillet until lightly toasted and pliable, or warm all at once in the microwave wrapped in a damp paper towel.
Divide the shredded cabbage, cooked fish, avocado slices, and chopped cilantro among the tortillas. Drizzle with the prepared sauce and serve with lime wedges for squeezing.