Sweet potato and lentil lasagne

• 1 tablespooon olive oil

• 1 brown onion, finely chopped

• 2 garlic cloves, crushed

• 2 zucchini, coarsely grated

• 400g sweet potato, peeled, coarsely grated

• 270g (1 1/4 cups) red lentils

• 625ml (2 1/2 cups) Vegetable Liquid Stock

• 700g bottle passata

• 375g packet fresh lasagne sheets

• 750g fresh ricotta, mashed

• 80g (1 cup) pre-grated cheese blend

• Baby rocket, to serve