Before you start, preheat oven to 220°C (or 200°C fan bake). Set aside a lined baking tray.
Heat oil in a large fry-pan on medium-high heat. Add beef and burger spices and cook, stirring, for4-5 minutes, until beef is browned. Add flour, stock, tomato sauce, mustard and salt and cook for a further 2-3 minutes, until slightly thickened.
Do not separate individual buns. Place hand flat on top of buns. Use a bread knife to slice through all of the buns horizontally, taking care not to pull them apart. Prep cheese and set aside.
Place bottom buns in lined baking tray. Top with an even layer of beef, pickles, cheese and top buns. Bake for 8-10 minutes, until cheese is melted and buns are golden brown.
Serve sliders on a tray with burger sauce on the side. Pull apart to serve.