In a small bowl, mix together 2 tablespoons of the mayonnaise , the chilli flakes, oregano and garlic. Season with freshly ground black pepper and spread over the chicken thighs. Cover with dry cling film and leave to marinate in the fridge for an hour, or longer if you have time
Mix together the chopped cherry tomatoes, avocado, sweetcorn and the rest of the mayonnaise. Season with black pepper and the lime juice.
Once marinated, barbecue the chicken over a medium heat for about 15 minutes, turning frequently. Remove from the heat and allow to cool for a few minutes before chopping roughly and stirring through the avocado mixture.
Spread the mixture evenly across half of each tortilla, sprinkle with grated cheddar and fold over the empty half of the tortilla to create a half circle, pressing down firmly.
Lay the quesadillas over the barbecue and grill over a medium heat for 2-3 minutes on each side, or until the cheese has melted and the tortillas are crisp.
Cut into wedges and serve immediately.