This is my approximation of the lovely dry-fried paneer served at Tayyabs, the famous Punjabi Indian place in East London. These amounts are for 1 as a main, or more as a starter. Takes about ten minutes:
First put the cubed paneer into a bowl, add the curry powder and cumin and toss to get an even coating.
Get a frying pan nice and hot, with about 1 tbsp of veg oil in it. Add the onion and chilli (and cumin seed if using). Note that you want the onion to be frying to be crispy at the end, so you want it finely sliced and separated (no big lumps), you want the oil hot, and you want the onion to have plenty of space in the pan. Fry it hot for about 4 minutes.
Add the paneer to the pan, and any spice left in the bowl. Shuffle it all around, it's time to get the paneer browning too. It'll take maybe another 4 minutes, not too long. Stir it now and again - it'll get nice and brown on the sides, no need to get a very even colour on all sides, but do turn it all around a couple of times.
Near the end, e.g. with 30 seconds to go, add the squeeze of lemon juice to the pan, and stir around. You might also like to sprinkle some garam masala into the pan too.
Serve the paneer with chive sprinkled over the top. It's good to have some bread to eat it with (e.g. naan or roti) and salad, or maybe with other indian things.