Cook spaghetti in salted water according to package instructions, drain. Meanwhile wash salmon, dab dry, cut into pieces of about 3 cm. Clean and wash spring onions, also cut into pieces.
Heat 1 tablespoon of butter in a frying pan. Fry the salmon for 2-3 minutes while turning. Season with salt, pepper and lemon juice. Sauté the spring onions in the cooking fat. Peel and finely dice the onion.
Melt 1 teaspoon of butter and sauté the onion. Stir in tomato paste. Add flour and sweat. Deglaze with cream and stock. Season with salt and chili. Let it boil for 2 minutes while stirring.
Place the noodles as nests on a small tray (28 x 22 cm). First spread salmon and spring onions, then the sauce on top. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for about 12 minutes.
Serve garnished with lemon and herb bouquet.