Remove the greens from your beets. If they're nice greens, you can cook them like you would chard or collards. Try not to throw them away if you can avoid it.
In a pot, submerge your beets in water and get the stove on medium. If the water does come to a boil before they're done cooking, cut the heat to a gentle bubble. Root vegetables tend to get kinda water-logged bu a vigorous boiling.
Now, how do you know when your beets are done?... Well, I can't give you an exact time because nature makes beets of all different sizes. To check if they're done, you'll need a thin, pointy object of some type. If it seems like it's been long enough for the cooking to get to the middle, stab your biggest beet. It should yield readily to the point.
Then you just strain and rinse them under cold water. The skin should peel off easily by hand.
Dice the beets to around 1/2" or so.
Julienne the shiso, not too fine, or it will bind up and get lost. Shuck the walnuts and break them up a bit. Toss it all together.
Add oil and vinegar and season to your liking with salt and pepper. Just try not to overpower that beet/shiso flavor.
