For the sauce, wash the lemon hot, grate dry, grate the peel thinly. Finely puree the ricotta, milk and cream. Season to taste with salt, nutmeg and lemon peel.
Clean, wash and grate the cauliflower on a coarse grater until it reaches the stalk. Wash, clean and dice all but one tomato. Peel and finely dice the onions and garlic. Wash oregano, shake dry.
Strip leaves from the stems except for a little bit for garnishing and chop them coarsely. Sort the spinach, wash and shake dry.
Heat 3 tablespoons of oil in a frying pan. Sauté the cauliflower and half of the onions for about 5 minutes. Add tomato pieces. Season with oregano, except for a little bit for sprinkling, salt and pepper.
Heat 2 tablespoons of oil and sauté the remaining onions and garlic until translucent. Add the spinach and let it collapse briefly in a closed pot. Season to taste with salt and nutmeg.
Oil an ovenproof dish (approx. 30 x 20 x 5 cm). Spread some sauce thinly on the bottom of the dish. Place 4 lasagne plates on top. Spread about 1/4 cauliflower and spinach on top. Put some sauce on top again and cover with 4 lasagne plates.
Repeat the process with 3 more layers of pasta. Spread the remaining sauce on the last pasta layer.
Grate the gouda and cut the mozzarella into slices. Cut the rest of the tomato into slices. Spread tomato slices and cheese on the lasagne. In a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see
manufacturer) bake for about 45 minutes until golden brown. Arrange the lasagne, sprinkle with oregano and garnish.