Top one half of each tortilla with cheese, chicken, green chiles and onions. Fold other half of each tortilla over filling; press down with back of pancake turner. Lightly brush melted butter on both sides of each filled tortilla.
Heat 12-inch nonstick skillet over medium heat. Cook 2 filled tortillas at a time 3 to 4 minutes, turning once, until golden brown and thoroughly heated. Cut into wedges. Serve with salsa.