Cut the buns in half horizontally. Roast the halves one after the other in the toaster until golden brown. In the meantime, heat 1 litre of water with vinegar and 1 tablespoon of salt in a saucepan. Beat the eggs individually in 4 cups. With a whisk create a whirl in the boiling water.
Slide the eggs individually into the middle of the strudel. Cook for about 4 minutes. Lift out the cooked eggs with a skimmer and let them drip off on kitchen paper.
Clean, wash and dry spinach. Heat the oil in a pot. Steam spinach for 2-3 minutes over a low heat while turning until it collapses. Season to taste with salt and pepper. Put 1/4 of the spinach and 1 poached egg on each of 4 toast roll halves.
Season with salt and pepper, cover with remaining toast halves.