Sauté the aromatics – In a large skillet over medium-high heat, add olive oil, onion, and garlic. Sauté for 5 minutes, stirring occasionally, until softened.
Toast the spices – Add chili powder, cumin, smoked paprika, onion powder, garlic powder, oregano, salt, and pepper. Stir frequently and sauté for 2 more minutes to bloom the spices.
Combine the filling – Transfer the onion and garlic mixture to a large mixing bowl. Add shredded chicken, refried beans, salsa, corn, and sour cream. Toss until evenly combined.
Prep oven and sheet pan – Preheat oven to 425°F. Lightly brush the bottom of a 13x18-inch sheet pan with melted butter.
Assemble the base layer – Arrange tortillas overlapping around the perimeter of the pan so that half of each tortilla hangs over the edge. Place two or three tortillas in the center to fully cover the bottom.
Add filling and cheese – Spread the chicken mixture evenly over the tortillas, then sprinkle the cheese blend evenly overtop.
Fold and seal – Place two more tortillas in the center, then fold the overhanging tortillas back toward the center to fully cover the filling. Brush the tops with more melted butter.
Bake and weigh down – Place a second large baking sheet on top to weigh it down. Bake for 20 minutes.
Uncover and finish baking – Remove the top baking sheet and bake for 5 more minutes, or until the top is golden brown and crisp.
Slice and serve – Let rest for a few minutes, then slice into squares and serve with sour cream, guacamole, or extra salsa!