Firstly, chop the paneer into square-shaped cubes.
After that, chop the capsicums and onions in square shapes and keep the chopped veggies and paneer aside.
In a large bowl, take the curd and whisk it till it becomes smooth.
Additionally, add roasted besan, ginger garlic paste, kashmiri red chili powder, cumin seeds powder, coriander powder, garam masala, black pepper powder, lemon juice, salt, sugar, kasuri methi, and mix well.
Further, heat up the mustard oil until it starts smoking, and then add turmeric powder.
Now add this hot oil to the marinade and spice mix.
Mix all the ingredients very well.
Further, add the capsicum, and onions and coat the all gently in the marinate.
Now add paneer cubes, and mix well gently.
Cover the bowl with a lid and let the paneer and veggies marinate for 4 hours or more in the refrigerator.