Clean the scallops and place each one back in its shell or in an oven-safe dish if shells are not available. Lightly season with salt and pepper.
In a small bowl, combine breadcrumbs, parsley, minced garlic, lemon zest, lemon juice, olive oil, and wine. Mix until evenly combined. You should get a soft paste.
Spoon the breadcrumb mixture evenly over the scallops, pressing lightly to adhere. Do not make the layer too thick. Add a thin slice on butter on top.
Place the scallops in the preheated oven and bake for 10-15 minutes, or until the breadcrumbs are golden brown and the scallops are opaque.
Serve immediately.
Notes
You can prepare the breadcrumb mixture and store it separately. Assemble the gratin just before baking for the freshest flavor and texture.