Preheat a frying pan. Halve the cabbage heads, then cut each half into 4 wedges, leaving core intact so wedges hold together. Place the cabbage wedges on the frying pan, and drizzle with vegetable oil on both sides. Sprinkle with sugar, salt, and pepper until *lightly* coated. Pan-sear (or grill) the cabbage for 4 minutes each side, or 8 minutes total, turning once or until the edges begin to wilt, but the bulk of the cabbage remains crunchy. Remove the cabbage from the pan and allow to cool a few minutes. Meanwhile, make the vinaigrette in a medium bowl. Prepare the orange zest by grating the orange peel from your orange. You need 1 tsp of zest for each serving of four so assume 2 tbsp if you're cooking for 20-24. Whisk the orange zest, Dijon mustard, and orange juice with the olive oil until it emulsifies. Add salt, and pepper, to taste. Chop the grilled cabbage, removing the core, and place in the bowl with the dressing. Add the parsley and green onion and toss to coat.