Bring the salmon fillets up to room temperature. This will ensure a more even cook.
In a frying pan over a medium heat, warm a little oil and add the salmon fillets, skin side down. Allow to cook gently while you cook the pasta and make the sauce.
Bring a pan of lightly salted water to the boil and add the spaghetti. Cook according to the instructions on the packet, or until al dente, about 8 to 10 minutes. Drain the pasta, reserving a ladle full of the water.
Meanwhile in a separate frying pan over a medium heat, warm a little oil then add the onions and mushrooms and cook and stir until soft, about 6 to 8 minutes. Season well and add a little lemon juice to taste. Add the cream cheese and stir to form a sauce.
Grill the bacon rashers, flipping once or twice to ensure that they are evenly cooked. Remove from the heat and chop. Set aside.
Check on the salmon fillets, flip once to brown the top for just a few minutes and remove from the pan once the salmon is evenly pink throughout and flakes easily with a fork. Flake the salmon and discard the skin and any bones. Set aside.
Add a little of the pasta water to the sauce and give a good stir, add more water, cream cheese or lemon to reach your desired consistency. Add the flaked salmon and the bacon along with the pasta and toss gently to coat. Serve immediately in warmed pasta bowls.
I may make this again but add something else like tomatoes or sweetcorn, maybe go totally crazy and have both. The best way I find is always taste at each stage if you are uncertain; never over-season.