Dab roulades dry if necessary and coat with mustard. Season with salt and pepper. Cut 12 thin strips from the bacon, dice the rest. Cut the cucumbers into quarters. Peel and quarter onions.
Place 2 strips of bacon, 1 onion quarter and 2 cucumber quarters on each roulade. Roll up the roulades firmly and pin them with roulade needles. Heat lard in a roaster. Fry the roulades in it all around.
Fry the remaining onions and bacon briefly. Add tomato paste and fry briefly. Deglaze with 500 ml water and beef stock, cover and cook for about 1 1/2 hours. Remove the roulades. Stir flour and a little cold water until smooth.
thicken the sauce with it. Bring to the boil again and season to taste.