Slice the onion thinly and mince the garlic.

Cut the salmon fillets into bite-sized pieces and season with salt and pepper.

Boil water in a pot, cook the spaghetti according to the package instructions, and drain.

Heat olive oil in a frying pan over low heat, add garlic, and sauté until fragrant. Add salmon and onion, and cook over medium heat until softened.

Add butter to the pan and melt over low heat. Stir in flour until fully incorporated, then add soy milk and bring to a gentle boil, stirring to thicken.