Blanch the greens for a minute or so in boiling water and then plunge in to cold water to arrest cooking. Once the greens are cold, drain them and squeeze them dry.
Sprinkle the greens with the salt and let sit for 30 minutes to an hour until they are wilted, then squeeze well to remove excess water.
Cut the stems into 3-inch pieces and then coarsely chop the leafy portion keeping the two separate for now.
Add the remaining greens along with the Mirin and the oyster sauce. Continue cooking until the sauce liquid is completely reduced then stir in the sesame oil, remove from the heat and allow to cool.
Garnish with Sesame Seeds before service if desired.