For the pesto basil, wash, shake dry and pluck leaves from the stalks. Coarsely grate the parmesan. Peel garlic and chop roughly. Put the basil, almonds, cheese and oil into a tall mixing bowl and puree finely with a blender.
Season with salt and pepper.
Briefly rinse a box mould (approx. 11 x 21 cm, 7 cm deep) with water and line it with foil. Clean and peel the carrots and cut or slice them lengthwise into very thin strips. Wash and clean the zucchini and cut or slice them separately lengthwise into very thin strips.
Lay carrots, green and yellow zucchini alternately in the mould. Spread each layer thinly with pesto. Cover with foil and weigh down. Chill for about 1 hour.
In the meantime, wash the parsley, shake dry and chop finely, except for a few leaves for garnishing. Season crème fraîche with lemon peel and juice, salt and pepper. Stir in chopped parsley, except for a few leaves for garnishing.
Peel onions and cut into thin rings.
Carefully turn the lasagne out of the mould. Carefully cut into pieces and arrange on plates, each with a dollop of crème fraiche. Sprinkle with onion rings and parsley and garnish.