Peel the garlic cloves, cut in half and remove the green sprout in the middle. Chop 2 garlic cloves and keep them apart. Salt and pepper the remaining 2 garlic cloves. Pierce the meat with a sharp knife and place half a clove in each slit.
Put the meat in a roasting tin with a bit of oil and place the potatoes around. Put the sliced onion in the gaps and add salt and pepper. In a blender beat the remaining oil with lemon juice, mustard, oregano, the finely chopped garlic and the vegetable stock cube dissolved in a ½ cup of hot water. Pour this over the meat and potatoes.
Cover the roasting tin with foil and roast at 180-200οC for 1 hour and 10 minutes. Remove the foil and sprinkle the cubes of cheese in the pan. Continue to cook for 10-15 minutes until both the lamb and cheese are brown. Sprinkle with the parsley and serve.