Put the beef on a baking tray. In a bowl, mix the ginger paste, garlic paste, salt, palm or cider vinegar, lime juice, turmeric, red chilli powder and oil to make a paste. Smoother the beef with the paste, wrap tightly in cling film and refrigerate overnight.
Preheat the oven to 110C/90C Fan/Gas ¼.
Remove the cling film from the beef and roast for 1 hour 40 minutes. When the beef is cooked, set aside to rest and drain the juices into a small saucepan. Simmer gently for 5 minutes.
To make the chilli fry, heat a deep-fat fryer to 180C. (CAUTION: hot oil can be dangerous. Do not leave unattended.) Fry the potato and carrot chunks for about 10–15 minutes, or until cooked through and golden-brown.
Meanwhile, heat a little oil in a frying pan. Once hot, add the cumin seeds, green chilli and garlic and fry for 5 minutes or until slightly coloured. Add the onions and fry until softened. Stir in the peppers and fry for 1–2 minutes, then add the tomatoes. Simmer for 3 minutes. Stir in the meat gravy and scatter with the coriander.
Slice the beef into cubes and stir into the vegetables until well coated. Check the seasoning and add salt and pepper as necessary.
Butter both sides of the toasted rolls and fill with the beef and vegetable mixture.