Slice the onion thinly and mince the garlic.

Pat the salmon dry with a paper towel, remove skin and bones, cut into bite-sized pieces, and season with salt and pepper.

Boil water in a pot, add salt, and cook spaghetti according to package instructions. Drain well.

Heat olive oil in a frying pan over medium heat, cook the salmon for about 2 minutes until done, then remove. Add onion and garlic to the pan and sauté until the onion softens.

Add flour to the pan and stir until no raw flour remains. Gradually add milk in three parts, stirring each time to thicken the sauce. Add salt and pepper to taste.

Combine the cooked spaghetti and salmon with the sauce, mixing well.