Preheat the oven to 180C / Fan 160C / 356F / Gas Mark 4.
To make the tomato sauce:
Fry the garlic in the oil for 1-2 minutes until softened. Add everything else and then simmer for 5 minutes.
To make the courgette filling:
Fry the onion and garlic in oil for 2-3 mins then add the courgette, carrot and spinach.
Fry for 3-4 mins until softened, add the vegetable stock cube (crumbled in), ricotta, Cheddar and milk and mix until combined.
To assemble:
In a large dish, layer the lasagne sheets, then courgette mix, then lasagne sheets, then tomato sauce.
Continue until you’ve used everything, sprinkle with cheese and then bake for 40-50 minutes.
Video
Notes
To make dairy free/vegan: Swap the milk for a dairy free one (like almond or soya), the cheese to a grated vegan cheese and ricotta for a vegan cream cheese.
To make ahead: You can construct this up to 24 hours in advance and refrigerate before baking. Alternatively construct in foil trays and freeze, than bake straight from frozen. Allow for extra time when doing this.
Leftovers: Can be kept in the fridge or frozen. Reheat thoroughly to eat.