Preheat the oven to 200°C.
Chop all vegetables into roughly equal-sized pieces.
Rub flour and butter together until the mixture resembles breadcrumbs.
Stir oats, cheese, pepper, and seeds into the crumble mixture.
Melt butter in a saucepan and sauté crushed garlic for one minute.
Stir in flour for one minute then gradually whisk in the milk or stock.
Season the sauce with salt, pepper, cheese, or lemon juice.
Cook fresh vegetables in the sauce for five minutes before adding frozen or optional ingredients.
Pour the mixture into a 20cm square baking dish and sprinkle the crumble on top.
Bake for 30 to 40 minutes until golden-brown and let cool slightly before serving.