While you're gathering ingredients, prepare the vegetables since this is the most time-consuming prep work. Finely shred the cabbage into 1/8-inch strips using a sharp knife or mandoline for uniform pieces that will dress evenly. Grate the carrots using the large holes of a box grater to create pieces that match the cabbage texture. Slice the scallions thinly, separating the white and green parts (you'll use both). Set all prepared vegetables aside in a large bowl.

In a medium bowl, whisk together the mayonnaise and Greek yogurt until smooth and well combined—I find Greek yogurt creates a tangier dressing with better body than regular yogurt, so don't skip this step. Add the rice vinegar, honey, and Dijon mustard, whisking until the mixture is completely homogeneous and the honey is fully dissolved. This ensures the sweetness and tang distribute evenly throughout. Season with salt, pepper, and celery seed, whisking one final time to incorporate the spices completely.

Pour the dressing from Step 2 over the prepared vegetables in the large bowl, reserving about 2 tablespoons of the white parts of the scallions for garnish. Toss everything together thoroughly, making sure every strand of cabbage and carrot is coated with the dressing. Taste a small bite and adjust the seasoning—add more honey if you prefer extra sweetness or a bit more salt if it needs more punch. I typically find the original measurements well-balanced, but personal preference varies.

Cover the bowl and refrigerate for 20-30 minutes to allow the flavors to meld and the cabbage to soften slightly while maintaining a pleasant crunch. Just before serving, give the coleslaw a quick toss and top with the reserved sliced scallion whites for a fresh garnish. The coleslaw will keep refrigerated for up to 3 days, though it's best enjoyed within the first day when the vegetables are crispest.