Butter 1 side of each tortilla.
Arrange 1 tortilla, buttered side down, in skillet or on cold griddle.
Layer cheese, chicken, onion and avocado over, leaving Winch border on all sides.
Drizzle evenly with salsa.
Top with remaining tortilla, buttered side up.
Cook over medium heat, turning once, until tortillas are golden, about 3 to 4 minutes per side.