Cook the spaghetti in boiling salted water according to packet instructions then drain, reserving a cupful of the cooking water.
Meanwhile heat a knob of butter in a frying pan and fry the trout fillets for about 3-4 minutes on each side until cooked through. Remove from the pan and set aside.
In the same frying pan heat another knob of butter and fry the garlic for a minute, then turn the heat down and add the cream cheese, lemon zest and plenty of seasoning to taste. Cook gently until you have a slightly thickened consistency.
Add the spinach, then tip in the spaghetti and add enough of the reserved cooking water to help the sauce coat the pasta well.
Remove the skin from the trout and flake over the spaghetti in the pan, allow to heat through briefly then divide between 4 bowls.