Preheat the oven to 450 degrees F. Brush a half sheet pan or rimmed cookie sheet with half of the butter.
Arrange 2 tortillas along the longest side of the sheet pan with half hanging over the rim; repeat with the other long side of the pan. Place one tortilla, also half hanging over, at each end. Place 1 tortilla in the center so the whole bottom of the sheet pan is covered.
Sprinkle evenly with half of the shredded cheese, all of the chicken, taco seasoning, chiles, corn and olives. Place spoonfuls of the salsa over the top and spread evenly. Top with the remaining cheese.
Place 1 tortilla in the center of the pan, on top of the filling, and then fold up the overhanging tortillas so that the filling is completely covered. Brush with the remaining butter, top with another sheet pan and press down firmly.
Bake until the tortillas are crispy and the inside is melted and hot, 20 to 25 minutes.
Carefully remove the top sheet pan. Slice the quesadilla into squares and serve with avocado, sour cream, lime and cilantro.