Preheat oven to 180 °C or 200 °C fan bake. Line 1-2 oven trays with baking paper.
Cook veggies
Peel and finely slice 1 brown onion. Peel and mince 2 cloves garlic . Finely dice 1 capsicum. Heat 1 tbsp olive oil in a large frypan on high heat. Cook the onion and garlic for 1-2 minutes, until softened. Then add the capsicum and 1 cup frozen corn and cook, stirring for 3-4 minutes. Sprinkle over 2 tbsp Mexican seasoning and add 400 g refried beans. Cook 1-2 minutes until heated through and well combined.
Make quesadillas
Lay half of the tortillas out on the prepared oven trays. Divide and evenly spread the veggie mixture over the tortillas. Grate 100 g cheese over the top of the veggie mixture and season with salt and pepper. Lay the remaining tortillas over top and press down firmly with a wide spatula or clean hands. Spray the tortillas lightly with oil spray.
Bake tortillas
Bake the tortillas in the oven for 10-15 minutes, or until golden and the cheese is melted. Switch the oven trays over halfway (if using more than one) for even cooking. Once cooked, remove from oven and slice into quarters.
Make salsa
Meanwhile, dice 2 tomato and 1 cucumber. Roughly chop 1 cup baby spinach. Roughly chop the coriander, discarding the stems. Add the tomato, cucumber, spinach and coriander to a bowl with 1 tbsp apple cider vinegar. Season with salt and pepper, add a pinch of chilli flakes (if using) and toss to combine. Put ½ cup sour cream in a small bowl.
To serve
Divide the cheesy corn and refried bean quesadillas between plates with the sour cream for dipping. Serve with the tomato salsa on the side.