Preheat an outdoor grill for medium heat and lightly oil the grate.
Melt butter in a frying pan over medium heat. Add onions and garlic; cook until soft and translucent, about 5 minutes. Remove from heat and stir in lemon juice and salt.
Place scallops in a large bowl and toss with butter mixture. Let stand for about 2 minutes.
Remove scallops from butter mixture, reserving excess in the bowl. Cook scallops on the preheated grill using a wire grill basket until golden, tossing occasionally for even cooking, 3 to 4 minutes.
Meanwhile, return butter mixture to the frying pan and bring to a boil over high heat. Reduce heat to low and keep warm while scallops cook. Toss grilled scallops in warm butter mixture and serve.
Grilled Bay Scallops · Dinner Match Lab | Dinner Match Lab