Preheat grill to medium-high heat.
Mix chili powder, paprika, cumin, garlic powder, salt, and pepper. Brush tilapia with vegetable oil and rub with spice mix.
Grill tilapia 4-5 minutes per side. Transfer to a plate and cover to keep warm.
Warm tortillas on the grill, 30 seconds per side.
Prepare the Creamy Lime Sauce: Whisk together sour cream (or Greek yogurt), lime juice, lime zest, salt, and pepper in a bowl. Set aside.
Break tilapia into chunks. Place on tortillas and top with cabbage or lettuce, avocado, tomatoes, onion, and cilantro.
Drizzle each taco with the creamy lime sauce. Serve with lime wedges for extra zing.