Roast the besan on a low flame for 2-3 minutes till it starts smelling nutty and turns a very light golden brown. Mix all the ingredients under marinade into a bowl and add paneer to it. Toss the paneer in the marinade till the cubes are coated well.
To add that distinct smoky tandoori flavour, heat a piece of lump coal till red hot. Place it in a steel bowl and place the bowl over the paneer. Add a teaspoon of oil to the coal. As soon as you start seeing smoke, cover the paneer. After five minutes of smoking, remove the coal, and marinate the paneer for half an hour or up to two hours.
Pre-heat oven to 220 C/ 430 F 10 minutes before ready to cook. Place a cooling rack over a roasting pan and set aside.
Skewer paneer cubes alternating with onions, capsicum and tomato (if using). This should make about 3-4 skewers.
Place the skewers on the cooling rack and bake for 15 minutes, turning once half way. After 15 minutes, switch on the broiler (or only the upper element of the oven) and broil for 2-3 minutes till the paneer has a slight char on the surface.
Carefully remove the roasting pan with the skewers out of the oven (the paneer tends to become really soft so be careful) and place the skewers on your serving platter. Top with chopped coriander and squeeze lime juice on them. Serve immediately with sliced onions.
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Notes
Make sure the paneer you are using is firm and not crumbly
If substituting paprika with Kashmiri Chilli Powder, the colour may be slightly different but the flavour should be the same
If the curds you are using are not thick enough, hang them in a muslin cloth for half an hour or so to remove whey and then use.
It is important to use hung curd or thick yogurt as this marinade will stick to the paneer. If the curd is loose, the marinade will not stick on to the paneer.
If you don't have an oven, you can grill it over a griddle pan as well. However, the taste and texture will not be the same as an oven or tandoor.