This is Pitaya. NOB we call it Red Dragon Fruit. Not only are they pretty, they are tasty as well. They are also very rich in vitamins, especially C. I think it tastes like an apple with a fruity, almost strawberry flavor. The meat is white and similar to a Kiwi. Except you have to eat the seeds. They are really tiny and scattered throughout the fruit in no discernible order.
They are seasonal here and available from August to October. They are so pretty I almost hate to cut them open! I've had more than one spoil because of this so now I eat them almost immediately after purchase. They usually cost around 10 pesos or a dollar each.
If you see them in your supermarket, give them a try. You'll be happy you added this to your list of edible fruits.