Wash the mushrooms and slice them. Peel and finely chop the onion. Sweat them in a sauté pan for 10 minutes with 3.4 fl oz of olive oil, salt, and pepper. Add the passata, season again, bring to a boil, and reduce for 5 minutes.
Remove the stems from the kale leaves and tear the leaves into small pieces.
Preheat the oven to 180°C (th.6).
Arrange a layer of lasagna sheets in an oiled baking dish. Cover with the mushroom sauce and spread some kale leaves. Drizzle with a little olive oil.
Add some pieces of gorgonzola and cover with another layer of lasagna sheets. Repeat the process until all ingredients are used, ending with gorgonzola.
Bake for 45 to 50 minutes, until the lasagna is tender and well gratinated.
Remove from the oven, sprinkle with basil leaves, and serve immediately.