Heat the oil in a large frying pan over a medium heat. Add the onions and fry for a few minutes.
Add the garlic, sweet potato, tomatoes, herbs, nutmeg and seasoning, and cover the pan. Simmer gently for 25 minutes until the sweet potato is just soft. Stir in the kale and beans.
Easy white sauce
Whilst the vegetables are cooking, add the cornflour, nutmeg and seasoning to a cold saucepan. Add most of the milk and stir to mix thoroughly, then slowly bring to the boil whilst stirring. Once the sauce is thick and smooth, add the remainder of the milk.
Add half of the sweet potato mix to a 20x30 cm baking dish. Add half of the lasagne sheets, breaking if necessary to fit in the dish. Add just under half of the white sauce and the cheese. Repeat with the remaining sweet potato mix, lasagne sheets, white sauce and cheese. Ensure that the top lasagne sheets are fully covered by the sauce. Bake at 180 degrees for 30 minutes.
Notes
For a vegan lasagne, use plant based milk and a good vegan cheddar.