Chop the leaves and stems of 2 bunches rainbow chard; keep separate. Heat 2 tablespoons toasted sesame oil and 4 sliced garlic cloves in a large pot over medium-high heat until golden. Add the chard stems and 1 sliced shallot; cook until just tender, about 4 minutes. Add the chard leaves and 3/4 teaspoon kosher salt; cook until tender, about 3 minutes. Top with toasted sesame seeds.