Step 1

Pour water into a large saucepan, wide skillet, or large wok to come 1" up the sides and place over medium-high heat. Mix white and pale-green parts of scallions, garlic, vinegar, oil, soy sauce, honey, and ginger in a small heatproof ramekin. Set inside a large bamboo steamer off heat (or, if using a metal insert, don’t bring water to a simmer and fit into saucepan before adding dressing. Cover dressing with foil.)

Step 2

Cut squash in half; scoop out and discard seeds. Slice into ½"-thick wedges. Arrange in steamer basket around ramekin, overlapping a little if needed (for metal insert, add as much squash as will fit without piling up, placing over dressing). Set over saucepan (or turn on heat), cover, and steam until squash is tender (a tester, skewer, or paring knife should easily slide through flesh), 13–15 minutes.

Step 3

Transfer squash to a platter and top with scallion greens and sesame seeds. Serve with dressing alongside.