Cut the pork into bite-sized pieces.
Thinly slice the onion.
Heat some cooking oil in a pan and stir-fry the pork.
When the pork is about halfway cooked, add the onion and stir-fry together.
Mix miso paste, soy sauce, sugar, mirin, and water to make the sauce.
Pour the sauce over the stir-fried ingredients and simmer.
Place the pork and onions over steamed rice.
Garnish with green onions to taste.