Pour beans into a shallow 2- to 3 - quart casserole. Stir in 1/2 cup salsa, 1 tablespoon of the lime juice, and the cilantro. Top bean mixture with corn, then sprinkle with cheese.
Bake in a 400 d F oven until mixture is hot throughout and cheese is bubbling, about 15 minutes. Meanwhile, stack tortillas and wrap in foil. Place in the oven until tortillas are warm, about 5 minutes.
While bean mixture and tortillas heat, pit and peel avocado. Cut into thin wedges and arrange on a small serving plate. Sprinkle avocado with remaining lime juice.
To assemble tacos, spoon bean and corn mixture into warm tortillas. Add avocado wedges and additional salsa to taste.