Preheat the oven to 200oC, gas mark 6. Grease and line a 22cm square tin.
Melt the butter in a frying pan and fry the leek for 3 minutes until softened. Mix into the oats with the walnuts, carrot, seeds, Cheddar and eggs, season. Press into the tin and bake for 25-30 minutes until golden.
Allow to cool slightly before cutting into 9 squares.
Cooks tip
Great for lunch boxes or on the go, or simply served with salad for a light lunch.