Riboflavin is a water-soluble B vitamin. In your body, riboflavin is primarily found as a component of coenzymes and works with the other B vitamins. Riboflavin is important for your body's growth, the production of red blood cells and healthy vision. It is relatively stable in vegetables. Without prolonged exposure to light, loss of riboflavin from cooking and storing is typically less than 15%.
Try to cook with a just single layer of vegetables in your pan at a time. Overcrowding prevents even cooking and you run the risk of ending up with mushy veg on the bottom.