Slice the onion into thin wedges and separate into individual pieces. If the pork is already chopped, then move on to the next step. If not, chop into large bite-sized pieces.
Chop the shiso leaves into strips of 2-3 mm. Soak in water, then drain.
Stir-fry the pork in a small amount of oil, then remove from the pan. Sauté the onion until translucent. Put the pork back in, turn the heat off, and mix in the shiso leaves. Dish it up.
It's tasty as-is, but I also recommend that you try it with ponzu sauce.
Story Behind this Recipe
My mother used to make this dish a lot. She didn't add onions, but I made this new variation to add lots of veggies.
The key is not to heat the shiso directly (residual heat is enough). If you are using pre-chopped pork, all you have to do is add it to the pan.
This recipe is especially a must when sweet (or new) onions are in season. -Sweet onions cook pretty fast. When you've cooked the meat in Step 3, don't worry about removing it - it's also fine to sauté the sweet onions with the meat still in the pan!