Soak wooden skewers in cold water for at least 30 minutes to stop them burning.
Cut all the vegetables into chunks, the onions should be cut into wedges and the button mushrooms can either be left whole or halved.
Thread the vegetables onto the skewers ensuring that each skewer has a wide variety.
Mix together the teriyaki sauce and brown sugar then brush generously over the vegetables.
Heat a griddle pan on a high heat and place the skewers into the pan.
Cook until charred on one side then turn. Continue until all sides have been charred and are caramelised. You can brush additional sauce onto the skewers as they are cooking if required.