Heat oil in a pan over medium heat, add the diced onion, and cook 3-4 minutes until translucent.
Add 250 g ground beef and cook 5-7 minutes, stirring occasionally, until browned and crumbly.
Stir in 4 tablespoon ketchup, 1 tablespoon mustard, the diced pickles, and season with salt, pepper, and paprika powder to taste.
Remove from heat and let cool to room temperature (about 10 minutes).
Quarter the 3 slices of cheese.
Roll out each piece of bread roll dough flat with a rolling pin.
Place 2 pieces of cheese in the center of each dough piece, add 1 tablespoon of the beef mixture on top, then fold the dough up and press firmly to seal.
Place the dough balls seam-side down on a baking sheet.
Lightly brush the top of each ball with water and sprinkle with sesame seeds.
Bake at 200°C (390°F) in a fan oven for 15-25 minutes until golden brown.