Preheat the oven to 175C.

Prepare the spinach. On medium heat defrost the leaves with water, mix to keep from boiling. Season, and move aside.

Make the tomato sauce.
- Chop the tomatoes into small cubes, and finely chop the cleaned chilli. Crush garlic cloves finely. Cut onion into small cubes.
- Heat a frying pan on high heat, add oil and the onion, garlic and chilli. Turn for few minutes, until onions start glisten.
- Add tomatoes, and keep on high heat. Keep on eye to keep from burning. Let simmer until the sauce thickens and some of the tomatoes can be crushed into paste. Season and check the taste. Move aside.

Start assembling the lasagna in a deep oven pan. First layer must be tomato sauce, then spinach, then lasagna sheets. Repeat these steps, spread pesto on the spinach, and press sheets on top of it. Finish with a layer of tomato sauce and grated mozzarella.

Cook in 175C oven for 30-40 minutes. Keep an eye on the lasagna. When finished, let first sit for 5 minutes before service.