Combine flour, cumin, salt and cayenne in a medium bowl. Whisk in beer to create a batter.
Dip tilapia pieces in the batter. Heat oil in a large nonstick skillet over medium-high heat.
Shake off excess batter and then add fish to the pan. Cook until crispy and golden, 2 to 4 minutes per side.
Place tortillas in a warmer like this one from Pfaltzgraff and microwave for one minute. Serve the fish with warm tortillas, Guacamole and Mango Salsa.