Bring first 3 ingredients to a boil; add mussels. Cover and cook 5 minutes; stir gently, and cook 5 more minutes or until mussels open. Remove from heat; drain and let cool. Discard any mussels that remain closed. Detach mussels from shells, reserving shells.
Combine mayonnaise and next 7 ingredients in a small bowl. Place each mussel in a shell; spoon 1 teaspoon Salsa Verde over each mussel. Place mussels on a platter, and garnish, if desired.