By keeping the food cooking in the wok close to 'dry' and by leaving it periodically unstirred - just cooking - you can sear the food in the wok without burning it. In mastering this aspect of how you cook with a wok, the trick is to keep on the edge of 'burning' by keeping the amount of moisture in the wok to a low level but not a zero level. The natural steam coming off of the vegetables in most wok recipes will keep a good hot steamy atmosphere inside the covered wok, but when this is not adequate, you will want to add a very small amount (5 ml to 10 ml at most) of water to the wok to refresh the hot steam under the dome of the lid.