Preheat oven to 350Â°F.
Spread a thin layer of salsa in a lightly oiled shallow baking dish.
Arrange 4 of the tortillas on top, overlapping as needed.
In a bowl, combine the refried beans with 1 cup of the salsa, stirring to blend well.
Spread the bean and salsa mixture over the tortillas and top with ½ cup of the shredded cheese.
Arrange the remaining 4 tortillas over the cheese and top with a layer of salsa.
Sprinkle the remaining 1/2 cup cheese on top. Cover and bake until hot, about 30 minutes.
While the casserole is baking, halve and pit the avocado and spoon the flesh into a bowl. Mash the avocado with the lime juice and salt and pepper to taste.
Serve with the casserole.