Pat fish dry; place in a large resealable plastic bag. Whisk together 3 tablespoons canola oil, 2 tablespoons lime juice, cocoa, ancho chile powder, cinnamon, and ¼ teaspoon each salt and black pepper. Add to bag. Seal bag; turn to distribute marinade. Let stand at room temperature for 15 minutes.
For slaw, combine sour cream, garlic and remaining ¾ teaspoon lime juice. Stir in cabbage, corn, cilantro, and jalapeno. Season to taste with salt and black pepper.
Heat remaining 1 tablespoon oil in a grill pan over medium-high. Remove tilapia from marinade. Cook 4 to 6 minutes or until fish flakes easily with a fork (145 degrees), turning once. Grill tortillas in a clean grill pan for 30 seconds or until slightly charred. Serve fish on tortillas with slaw and avocado. Garnish with cilantro and jalapeno slices, if desired. Serve with lime wedges.
