Preheat oven to 500F. Lightly grease a baking sheet with cooking spray and set aside.

Add vegetable broth to a soup pot and bring to a boil. Add the mussels; cover with a lid and continue to cook over high heat for 4 minutes, or until they open. Using a slotted spoon, transfer mussels to previously prepared baking sheet. Remove from heat.

Melt butter over medium-heat in a nonstick skillet. Add garlic and cook for 3 minutes, or until lightly browned, stirring very frequently. DO NOT burn the garlic. Stir in the rosemary, and continue to cook for a few more seconds. Remove from heat.

Add panko crumbs, salt and pepper; stir until moistened and well combined. Spoon prepared crumbs over the mussels.

Transfer to oven and bake for 4 minutes. Remove from ovent. Garnish with chopped fresh parsley. Serve.