Place top oven rack in the center position and pre-heat to 400°F. Line a large, rimmed baking sheet with parchment paper or a Silpat™ baking mat. 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 two tablespoons balsamic vinegar. Sprinkle with garlic powder and season with salt and black pepper, to taste.

Place the baking sheet in the pre-heated 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.

Fifteen minutes before the cabbage is ready, heat the remaining balsamic vinegar over medium-high heat just until it begins to boil. Immediately reduce heat to just below medium and simmer, stirring continually, until the liquid is reduced to about 1/3 of its original volume, approximately 8-10 minutes. Reduce heat to low to keep warm until ready to use.

Remove the baking sheet from the oven and cool for several minutes. Drizzle each cabbage steak with the warm balsamic glaze and top with some pomegranate arils and toasted sunflower seeds. Serve immediately with the roasted red onion on the side. Enjoy!