Peel the garlic for the sauce. Puree the ricotta, crème fraîche, milk and 1 garlic clove with a hand blender. Stir in lemon zest. Season to taste with salt, pepper, 1 tsp. paprika and nutmeg.
Clean and wash the cauliflower and grate it coarsely all the way to the stalk. Wash the tomatoes. Slice 1 tomato, cut the rest into small pieces. Peel and finely chop the onions. Wash oregano, shake dry, chop leaves roughly. Wash spinach and spin dry.
Heat 3 tablespoons of oil in a large frying pan. Fry the cauliflower and half the onions for about 5 minutes in portions, turning them over. Add tomato pieces and oregano. Season to taste with salt and pepper. Take out and wipe out the pan.
Heat 2 tablespoons of oil in a frying pan. Finely chop the remaining clove of garlic. Fry with the rest of the onions until translucent. Add the spinach. Cover and let it collapse in about 3 minutes. Season with salt and nutmeg.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Oil an ovenproof dish (approx. 5 x 20 x 30 cm). Spread approx. 4 tbsp. ricotta sauce in the dish. Place 4 lasagne plates on top. Place approx. 1⁄4 cauliflower mince, 1⁄4 spinach, some sauce and 4 lasagne plates on top. Repeat three times, dripping the rest of the sauce onto the last layer of pasta.
Grate the gouda and cut the mozzarella into slices. Spread the tomato slices and cheese on the lasagne. Bake in a hot oven for about 45 minutes.