To prepare a vegetable tempura recipe, you'll first need to prepare the vegetables. You can use any type of vegetable you like, as long as it isn't too tough or mushy. If you want to make your own, use whatever you have on hand, or you can buy pre-made vegetables at your local grocery store. Place the vegetable in the bottom of an oven-proof dish and bake it for 10 to 15 minutes. Remove the dish from the oven and let it cool for 5 to 10 minutes before slicing it into bite-sized pieces.