Cooking mussels on the grill is easier than you'd think and it puts a summery meal on the table in under 30 minutes.
Heat a grill or grill pan to medium-high. Clean and lightly oil hot grill. In a small pot, melt butter over medium. Remove from heat and stir in parsley; set aside.
Working in batches if necessary, place mussels on grill in a single layer. Place lemons, halved and lightly oiled, on grill, cut side down.
Grill until mussels open and lemons are warmed through and browned, 5 minutes. With tongs, transfer mussels as they open to a large platter. (Discard unopened mussels.) Pour herb butter over mussels; sprinkle with salt and pepper. Serve with lemons.