Melt butter in a non-stick frying pan over medium-high heat. Add bacon and cook 1 minute or until it starts to colour. Add the mushrooms. Cook, stirring for 3 minutes or until mushrooms are tender.
Whisk the eggs and milk together until well combined. Pour the eggs over the mushrooms and stir gently with a wooden spoon for 1 minute until they start to set. Remove the pan from the heat just before the eggs are completely set as they will continue to cook in the warm pan.
Put the tortillas on the clean bench. Spoon ¼ of the mushroom egg mixture on one half of each tortilla. Top with ¼ of the cheese, fold tortilla in half to cover egg and cheese.
Wipe the frying pan clean with paper towel. Preheat pan on medium. Lightly spray quesadillas with oil, cook 1 at a time for 3-4 minutes until the base is golden. Carefully turn over and cook a further 3 minutes. Cut the quesadillas in half and serve with avocado, parsley & yoghurt.