Bring a large pot of water to boil, season with salt. Add spinach and cook until just wilted, about 30 seconds. Drain immediately in colander and plunge into ice water.
Let spinach cool completely, about 30 seconds, drain again. Using your hands, squeeze excess water out of spinach. When you think you are done squeezing, do it one more time. Spinach is absorbent stuff. Transfer to cutting board.
Coarsely chop spinach and place in medium bowl, set aside.
Meanwhile, whisk together oil, soy sauce, and rice vinegar. (I do this while the water is boiling). Add dressing and sesame seeds to the spinach, mix to combine.
Spinach may be refrigerated for up to 2 days. I, however, have trouble not eating it between mixing in the sesame seeds and putting it on the plate, that’s how good it is. If you love spinach, that is.