Preheat oven to 175°C / 350°F. Get ready a ramekin that can hold 350ml of liquid (1 1/2 cups).
Filling
Heat a frying pan over medium heat. Add in bacon and cook until bacon is crispy. Remove with a slotted spoon and transfer the bacon into the ramekin. Drain until there's about 1/2 tablespoon of bacon fat left in the frying pan.
Add in the onion and cook until it is soft, then add in the mushrooms and vegetables. Cook over medium heat, tossing frequently, until the mushrooms are browned and have shrunk in size and the vegetables are soft. Season lightly with salt and freshly ground black pepper. Transfer the cooked vegetables into the ramekin.
Custard
Whisk cream egg, herbs, salt, black pepper and cheese in a small bowl. Pour the mixture into the ramekin.
Bake
Bake for 25 to 35 minutes until the quiche is almost set - the center will jiggle slightly. Remove from the oven and set aside for 10 minutes to cool slightly before serving.
NOTES
Use whatever herbs you like - parsley, oregano, thyme etc. I used a pasta herb mix.
I like to use a mix of mozzarella, cheddar and Parmesan but you can use whatever cheese you like - emmental, swiss, gruyere etc.
To make this ahead, you can prepare the filling and custard separately the night before and store in the refrigerator. The next day, while the oven is heating up, assemble them in the ramekin then send them off to the oven!