Peel and chop the onion. Knead with minced meat, mustard and egg. Season with salt, pepper and paprika. Form to 4 meatballs and fry in hot oil while turning for about 12 minutes
Wash the lettuce leaves and shake dry. Cut out thick ribs of leaves Clean and wash the tomatoes. Cut tomatoes into 1/2 cm thick, cucumbers into fine slices
Divide the baguette into 4 equally sized pieces and cut them open. Spread the lower halves with mayonnaise and cover with lettuce leaves, cucumber and tomato slices
Cut through the meatballs horizontally. Place 2 halves on each baguette. Grate cheese on top and sprinkle with roasted onions. Put the baguette lid on top