Preheat oven to 400°F. Line a large rimmed baking sheet with foil, parchment paper or a silicone baking mat; coat lightly with olive oil cooking spray.
Remove any damaged outer leaves from cabbage and cut into 8 wedges, keeping the core intact to hold them together. Arrange the wedges on the prepared pan. Coat the tops of the wedges lightly with cooking spray and season with ¼ teaspoon salt and pepper to taste.
Roast the cabbage, rotating the pan from back to front and flipping the wedges halfway, until tender and golden, 30 to 40 minutes.
Meanwhile, combine oil, vinegar, lemon juice, mustard, garlic, the remaining ¼ teaspoon salt and pepper to taste in a jar with a tight-fitting lid. Cover and shake until well blended.
Let the cabbage cool for 5 minutes, then coarsely chop. Transfer to a shallow serving dish and drizzle with the dressing. Sprinkle with almonds and chives (or parsley) before serving.
