Heat the olive oil in a skillet over medium heat. Stir in the garlic and onion; cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in the tomato and cook until softened, then add the salmon. Flake the salmon and continue cooking for 3 minutes. Stir in water, bay leaf, salt, pepper, and fish sauce. Bring to a simmer. Cover and cook for 20 minutes.