Leek And Potato Gratin

• 3 matzos
• 2 leeks
• 1 bell pepper (red)
• 1 salt and pepper
• 1 chives for top (minced)
• 240 ml water (hot)
• 170 ml evaporated skim milk
• 110 gr mozzarella (grated)
• 28 gr margarine
• 4 slices potatoes