Potatoes Nicoise

• 3 1/2 tomatoes
• 3 sprigs parsley (fresh)
• 1 garlic clove
• 1/2 potatoes a prepared casserole dish (into)
• 1/2 parsley mixture
• 1/2 onions
• 900 gr shallow baking dish
• 28 gr low fat margarine
• 6 gr salt
• 3 gr salt