Sea Island Steamed Mussels

Name: Sea Island Steamed Mussels
Ingredients: 2 tablespoons unsalted butter; 1 small yellow onion, sliced; 2 cloves garlic, minced; One 14.5-ounce can diced tomatoes; 1/8 teaspoon cayenne; Kosher salt; 1/2 cup sparkling wine; 1 pound mussels (preferably cultivated), scrubbed well and beards pulled off; 2 tablespoons chopped fresh parsley; 2 lemon wedges; Grilled Garlic Bread, recipe follows; 4 slices day-old bread; 4 tablespoons unsalted butter, at room temperature; 1/2 teaspoon Italian seasoning; 1/2 teaspoon garlic powder