Cut the roast every approx. 2 cm, but do not cut all the way through. Brush the gaps with mustard. Put the meat in a baking dish.
Mix the sweet and sour cream with the pressed garlic, pepper and parsley. Pour over the meat and leave to stand in the refrigerator for 24 hours, covered.
Clean and dice onions, peppers, carrots and zucchini. Put in a pan with heated olive oil and sauté. Season to taste with mustard and garlic, pepper and possibly salt and chili powder.
Now pour this vegetable mixture over the meat.
Cook in a preheated oven at 180 degrees for approx. 90 minutes.
Then crumble the feta cheese, spread it on top and place in the oven until the feta has melted.