Inspired by fajitas, these sheet pan quesadillas tuck bell peppers and onions into the tortillas, along with plenty of cheese. The key to the flavor is the homemade fajita seasoning that uses just a few spices that you probably already have in your pantry. Whisk those together and prep the fillings, then you can bake the quesadillas on a sheet pan and serve them all at once!
Preheat the oven to 425 degrees F. Line a large rimmed baking sheet with parchment paper.
Make the seasoning: Whisk together the chili powder, smoked paprika, onion powder, garlic powder, cumin, sugar, and salt in a small bowl. Set aside.
Make the quesadillas: Heat the oil in large nonstick skillet over medium-high heat. Add the turkey and cook, breaking up the meat, until the turkey is no longer pink and most of the liquid has evaporated, 4 to 5 minutes. Stir in the fajita seasoning, sour cream, bell peppers, and onions and cook on medium-high heat, stirring occasionally, until the onions are tender, 4 to 5 minutes.
Assemble and bake the quesadillas: Spread a thin layer of mayonnaise onto 2 of the tortillas and arrange them mayo-side down on the prepared baking sheet (this will help the tortillas brown), then sprinkle with half of the cheese edge-to-edge. Top with the filling then repeat sprinkling with the remaining cheese. Cover each quesadilla with 1 of the remaining tortillas and spread a thin layer of mayonnaise on top. Place another piece of parchment paper directly on top of the quesadillas followed by another large baking sheet to weigh them down.
Bake 15 to 20 minutes, until the cheese is melted and the tortillas are crispy. Cut into wedges and serve warm.