Drain the tomatoes. Cut ham and tomatoes into cubes and mix with 100 g cheese and pizza spice mixture. Wash the meat, dab dry and cut lengthwise for filling (do not cut through).
Season with salt and pepper. Spread the stuffing evenly over the roast and pin the cut opening with wooden skewers and tie up with kitchen string. Place roast in the greased fat pan of the oven.
Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 1 hour. Wash the potatoes and cook in plenty of boiling water for about 20 minutes. Rinse under cold water, drain and peel.
Clean and wash the spring onions and peppers. Cut spring onions crosswise in half, cut bell peppers into large cubes. Wash, clean and quarter the tomatoes. Wash oregano, shake dry and pluck leaves from the stalks.
1/2 hour before the end of the cooking time, spread the remaining cheese on the roast and vegetables around the roast. Season vegetables with oregano, salt and pepper. Cut the potatoes into pieces. Heat clarified butter in a pan.
Fry the potatoes in it until golden brown, turning them over. Season with salt and pepper. Take the meat out of the oven, let it rest for a short time and cut it into slices. Arrange meat and vegetables on a plate. Add the potatoes.