1. Preheat the oven to 200°C (gas mark 3, convection oven: 180°C). Wash the potatoes and cut them into quarters with the skin on. Mix 2 tsp of oil with salt, pepper, and 1/2 tsp of paprika powder. Mix everything with the potato quarters and spread them on a baking sheet lined with parchment paper. Bake the potatoes for about 35 minutes on the middle rack of the oven. Cut 1 tomato and the pickles into slices, then cut the remaining tomatoes into quarters.
2. For the sauce, mix the ketchup and mustard. Season with salt, pepper, and a little Worcestershire sauce. For the burgers, cut half of the onion into rings and the other half into small cubes. Mix the ground meat and onion cubes. Season with salt, pepper, and the remaining paprika. Shape into 4 flat burgers. Heat the remaining oil in a pan. Fry the burgers for 3 to 5 minutes on each side.
3. Cut the hamburger buns and spread sauce on each half. Place tomato slices, pickles, and onion rings on the bottom half. Place the burger on top, cover with cheese, and sprinkle with fried onions. Cover with the top half of the bun.
4. Season the tomato quarters with salt and pepper. Serve with the ground meat burgers, potatoes, and the remaining sauce.