Preheat the oven to 400 degrees F. Lightly grease a sheet pan with olive oil.
Tear the wilted outer leaves off the cabbage. With the cabbage stem side down, cut it in half. Then cut each of those halves into 4 wedges, so you end up with 8 cabbage wedges.
In a small bowl, whisk 2 tablespoons olive oil and 1 tablespoon rice vinegar.
Put the wedges on the sheet pan in a single layer without touching or overlapping. Brush the cabbage all over with the oil-vinegar mixture and sprinkle with salt and pepper.
Roast the cabbage for 20-25 minutes until browned in spots and caramelized at the edges, flipping over halfway through roasting.
For the tahini sauce, puree the garlic, tahini, parsley leaves, scallions, soy sauce, lemon juice, pinch of salt, 1/4 teaspoon pepper and water in a food processor or blender until combined and smooth. It should have a thick, but slowly pourable/spoonable consistency. Add a little more water as needed.
Arrange the cabbage on a serving platter. Drizzle with the tahini sauce and sprinkle with sesame seeds and chopped parsley.