There are several reasons why your vegetables might turn out soggy in a stir fry: 1) you overcooked them - stir fry at medium-high heat for a short time, not low heat for a long time. 2) you added too much liquid - only add liquid at the end, not much of it. 3) you overcrowded the pan - use a large pan or fewer veggies. 4) you didn't stir enough - stir fry requires almost constant stirring of the veggies so that the steam gets out of the pan and the veggies scorch evenly on the hot pan without getting soggy.