Take the vegetable oil, and heat it on a skillet that is over a medium heat. Stir in the onion now, and cook this until it is tender. Now you can mix in your ginger and garlic, and continue to cook on the skillet for another minute. Mix in your potatoes, carrots, jalapeno, cashews, and tomato sauce now. Be sure not to forget to season this with salt and curry powder! Cook this altogether, stirring all the while, for about 10 minutes, or until the potatoes are tender.