In a large saucepan cook the stir-fry vegetables and jalapeno in hot margarine for 3 to 5 minutes or until tender. Stir in flour. Stir in milk and half and half. Cook and stir until slightly thickened. Cook and stir 2 minutes more.
Stir in potatoes, salmon, watercress, lemon juice, salt and pepper. Cook and stir until heated through.