Whisk sour cream with juice of 1 lime and a pinch of salt to make crema; thinly slice cabbage and dice mango, toss together with juice of 1/2 lime for slaw.
Pat tilapia dry, brush with olive oil, season with chili powder, and pan-fry over medium-high heat for 3 minutes per side (145°F internal temperature); break into bite-sized pieces.
Warm tortillas in a dry skillet over medium heat for 30 seconds per side.
Build tacos with tortillas, tilapia, mango slaw, and lime crema drizzle; serve immediately with extra lime wedges.