Add the lentils to a large casserole tray, spread over the base.
Then spread the caramelised onions over the lentils.
Top with the mashed veg, spreading out to cover everything.
Sprinkle with the walnuts (brake up a little) and a drizzle of olive oil
Bake for 20 minutes on 180c.
Remove from the oven to cool a little.