Cheesy French Onion Cabbage

Name: Cheesy French Onion Cabbage
Ingredients: 1 large head green cabbage , cut into 8 wedges with core intact; 5 tablespoons extra-virgin olive oil , divided; ½ teaspoon garlic powder; ½ teaspoon salt; ½ teaspoon ground pepper , divided, plus more for garnish; 1 large sweet onion , halved and thinly sliced; 2 teaspoons chopped fresh thyme , plus fresh thyme leaves for garnish; 1½ teaspoons reduced-sodium soy sauce; ¼ cup reduced-sodium vegetable broth; 1 tablespoon sherry vinegar or cider vinegar; 1 cup shredded Gruyère cheese