Thin flakes of dried bonito, a fish that's related to mackerel and tuna, have been used as a briny, faintly smoky seasoning in Japan for centuries. Bonito flakes are available at most natural grocery stores.
-Bring a large pot of water to a boil.
-Wash 1 bunch of rainbow chard, leaving the leaves whole.
-Add the chard leaves to the boiling water and cook, until barely tender, 3 to 4 minutes.
-Drain, then submerge chard in a bowl of ice water.
-When chard is cool, drain again, squeeze out excess liquid, and cut into bite-size pieces.
-Toss chard with 2 TBS soy sauce and top with 1 TBS bonito flakes.
-Divide among 4 bowls.