Rinse fish and pat dry; then place pieces side by side in an ungreased 8x12-inch baking dish. Pour salsa over fish. Sprinkle evenly with cheese, then with corn chips.
Bake, uncovered, in a 400 degree oven until fish is just slightly translucent or wet inside; cut in thickest part to test (12 to 15 minutes). Meanwhile, pit, peel, and slice avacado.
Garnish fish with avacado slices. Serve with sour cream, if desired; offer lime wedges to squeeze over fish to taste. Makes 4 servings.