Heat 2 tablespoons of olive oil in a pot and fry onions and garlic. Add peeled tomatoes, spices, capers and lemon peel. Mash tomatoes roughly with a spoon, cover the pot and let simmer for about 10 minutes. In the meantime heat remaining olive oil in a pan and fry the mushrooms for about 2 minutes. Season with salt and pepper. Serve spaghetti along with sauce and mushrooms. Sprinkle with cashew nuts and basil leaves.