Peel vegetables and cut into even sized chunks. Place in a roasting tray, drizzle with olive oil and season. Place in a pre-heated oven Gas 6 400F 200C for around 15 minutes until just softened when tested with the point of a knife, and caramelising round the edges.
At the same time, spread oats on a baking sheet and toast in the oven for around 5 minutes, until golden brown.
For the sauce, melt butter in a pan and add flour. Cook over gentle heat for a minute. Remove from heat and gradually add milk, stirring. Return to heat and continue cooking until thickened and smooth, still stirring. Add 100g/4oz cheese and stir to melt. Add parsley. Season with salt and freshly ground black pepper
Place vegetables in a pie dish and pour over sauce. Tip toasted oats into a bowl and add remaining cheese. Sprinkle over vegetables. Bake in a pre-heated oven Gas 6 400F 200C for around 15 minutes, or until top is crunchy and brown.