Though this is optional, I tend to do this with store bought paneer. I cube them, place them in a bowl and pour some boiling water on top - enough to cover the paneer. I let it sit for about 30 seconds or so and drain the water. I do this 'cos I find that not only does it make the paneer soft but it also gets rid of impurities, if any. Don't soak for long otherwise the paneer will get mushy.
Make sure to keep all the chopped Vegetables and sauce nearby. From here on, since the cooking is on high heat, everything needs to go in quick. Delay will cause the food to burn. Heat a wok medium - high heat and when hot, add butter and oil. Drop the paneer and saute it for 1 min or so.
Stir it occasionally until you see it browned/golden. It enough even if its only one side.
Increase the heat to little less than high and drop the onion along with the paneer.
Keep stirring for 10-15 seconds and then add the carrots, bell pepper, celery and onion whites.
Stir until you find the vegetables softening lightly. The vegetables should still be crisp. Next add the soy sauce and keep stirring until the sauce is well combined.
Stir to combine. Taste to see if it needs salt and adjust accordingly. Add pepper.