Prepare Tomato and Avocado Salsa, if using.
Combine flour, cumin, salt and cayenne in a medium bowl. Whisk in beer to create a batter.
Coat tilapia pieces in the batter. Heat oil in a large nonstick skillet over medium-high heat. Letting excess batter drip back into the bowl, add the fish to the pan; cook until crispy and golden, 2 to 4 minutes per side. Serve the fish with tortillas and salsa.
Combine tomato, onion, jalapeno, lime juice to taste, salt and pepper in a medium bowl. Stir in avocado and cilantro. Add cayenne (if using).