Preheat oven to 350°F. In a small skillet over medium-low heat, melt butter. Add garlic and cook, stirring, until fragrant, 30 seconds. Add bread crumbs, stir to coat with butter, then cook, stirring frequently, until light golden brown, about 5 minutes. Remove from heat and stir in parsley and lemon zest. Let cool. Combine mustard and mayonnaise in a small bowl.