Preheat oven to 450 degrees f.
Cut the cabbage into wedges, then arrange it on a baking sheet.
Brush both sides of each cabbage wedge with oil. Sprinkle garlic powder, red pepper flakes, sea salt, and pepper over each wedge.
Roast in the preheated oven for 15 minutes; flip cabbage and continue roasting until a bit browned and charred in some areas, about 10-15 minutes more.
Squeeze lemon over each wedge.