Heat oil in a large nonstick skillet over medium-high heat. Add bell pepper, onion, and fish; sauté 3 minutes. Add beer; cook 5 minutes or until liquid evaporates and fish flakes easily when tested with a fork. Remove from heat; stir in salt and pepper. Set aside, and keep warm.
Wrap tortillas tightly in foil, and bake at 350° for 10 minutes. Divide fish mixture evenly among tortillas, and roll up.
Arrange 2 fajitas on each of 6 plates; top with 1/3 cup Tomatillo Guacamole, 1/4 cup salsa, and 1 tablespoon sour cream.