Preheat oven at 190° C.
Heat the low-fat spread and soften the chopped onion over medium heat, without allowing it to brown.
Add the crushed garlic, chopped tomatoes and lemon juice.
Season to taste with salt and pepper and stir well.
Spoon about one-third of this sauce into a shallow ovenproof dish.
Arrange the cod filets on top, then pour over the remaining sauce.
Cover the dish with a lid or with aluminum foil and bake in a moderately hot oven for 25-30 minutes.
Remove from the oven and sprinkle over a little chopped parsley to garnish before serving.