Preheat the oven to 400°F. Cut the stem off the cabbage so it sits flat.
Whisk together mustard, maple syrup, Worcestershire, garlic powder, salt, and pepper in a medium bowl. Set aside.
Combine the celery, carrots, onion, and chopped herbs in a large bowl. Spray them with zero-calorie nonstick cooking spray and season with salt and pepper. Toss to coat.
Place the vegetable mixture in a large, oven-safe skillet. Nestle the cabbage in the center, on top of the vegetables. Pour ¼ cup of vegetable broth into the bottom of the skillet and cover the cabbage with aluminum foil. Bake for 45 minutes.
Remove the foil and add the remaining ½ cup of broth and bake until cabbage is tender and slightly charred, about 45 minutes.
In a saucepan, mix the gravy ingredients and pour over the cabbage and vegetables when ready to serve.