Prepare the pasta in boiling salted water according to the instructions on the packet. Peel and finely chop the onion. Wash the zucchini, quarter them lengthwise and cut into pieces. Melt butter in a pot. Sauté onion and zucchini in it, add stock and cream, bring to the boil and simmer for 5 minutes. Wash the thyme, put something aside for garnishing.
Pluck the remaining leaves from the stems and chop finely. Add thyme to the zucchini. Stir in the sauce thickener and bring to the boil again. Season to taste with lemon juice, salt and pepper. Drain the pasta and arrange on plates with the sauce and salmon. Serve garnished with thyme and lemon slices