Grate rind from lime, and squeeze juice to measure 3 tablespoons. Place rind and juice in a 1-gallon zip-top freezer bag. Add cumin and oil. Seal bag, and shake to combine. Add fish to marinade. Reseal bag, and turn to coat fish. Chill several hours.
Heat a large cast-iron or nonstick skillet over medium-high heat until hot. Add fish, and cook 10 minutes or until browned on all sides. Remove each piece of fish from skillet when it is done. (Do not overcook.) Break fish into smaller chunks.
Toast tortillas on both sides in a large skillet over medium heat while fish cooks. Cover tortillas, and keep warm.
Spoon fish into tortillas; top with Jicama-Cilantro Coleslaw and Fire-roasted Tomatillo-and-Poblano Salsa. Garnish, if desired.