Place top oven rack in the center position and pre-heat to 400°F. Line a large, rimmed baking sheet with parchment paper. Set aside.
Cut the stem off the cabbage head to create a flat surface on the bottom. Carefully slice the cabbage, top to bottom, into ½-inch sections.
Transfer the sliced cabbage to the prepared baking sheet and arrange the onion wedges between them without overcrowding. Lightly brush the cabbage and onion with the olive oil and one tablespoon of pomegranate molasses. Sprinkle with garlic powder and season with salt and black pepper, to taste.
Place the baking sheet in the preheated oven and roast for 40-45 minutes, rotating the sheet once halfway through, or until the cabbage is nicely browned and crispy on the edges.
Remove the baking sheet from the oven and cool for several minutes. Drizzle each cabbage steak with the remaining two tablespoons of pomegranate molasses and top with some pomegranate seeds and toasted sunflower seeds. Serve immediately with the roasted red onion on the side. Enjoy!
Actual cook time will depend on how thick and evenly the cabbage is sliced, and on how much moisture is in the cabbage from the outset. Check after 30 minutes and adjust the final cook time accordingly.