1. Preheat your oven to 400°F (200°C).

2. Sauté the onion and garlic in butter in a large skillet until softened without browning.

3. Add crushed tomatoes, water, lentils, vegetable broth, and vinegar to the skillet. Season with sugar, thyme, salt, and pepper, then bring to a simmer and let cook for about 10 minutes.

4. Stir in the spinach and adjust seasoning as needed.

5. In a separate pot, cook the lasagna sheets according to package instructions, then drain and set aside.

6. In a greased 23x33 cm (9x13 inch) baking dish, create a layer of the lentil sauce.

7. Arrange one lasagna sheet on top, followed by a layer of the sauce and half of the cheese (a Swedish cheese that can be substituted with a similar sweet and sharp cheese, such as a combination of cheddar and feta).

8. Repeat this process, finishing with a layer of sauce and the remaining cheese.

9. Cover the dish with aluminum foil and bake for 20-25 minutes.

10. Remove the foil and bake for an additional 5-10 minutes, or until the cheese is golden brown and bubbly.

11. Remove from the oven and let it rest for a few minutes before serving with a side salad and garnished with fresh basil leaves if desired.