Place 4 tortillas on a baking sheet greased with cooking spray or lined with parchment paper. Divide the cheese among the tortillas, sprinkling it evenly onto each tortilla. Sprinkle the seasoning salt over the cheese and then top with the green onions. Top each with the remaining 4 tortillas. Bake until the cheese is melted.
Remove the quesadillas from the oven and slice into quarters. In a large skillet, melt 1 tablespoon of butter over medium-high heat and add 4 pieces of quesadilla. Toast the pieces in the pan until crispy and golden. Repeat with the remaining 3 quesadillas. Serve warm with salsa and guacamole.