Mix the flour, salt, curry powder, and cayenne pepper together in a large bowl. Add the scallops to the bowl and toss the mixture together until you thoroughly coat the scallops in the spiced flour mixture.
Melt the butter in a large skillet over medium-high heat. Add the scallops to the butter and sauté them, turning once, until they are golden brown on both sides, about 4 minutes; transfer the scallops to a plate and cover to keep warm.
Add the mushrooms and onions to the skillet and sauté, frequently stirring, over medium-high heat for 4 minutes, until they start to turn light brown. Add the white wine to the pan and scrape the bottom of the pan with a metal spatula to get all the brown bits off the pan and into the sauce. Reduce the heat slightly and simmer until the sauce has reduced by half. Remove the pan from the heat and stir in the Cognac and scallops.
Preheat the oven broiler. Divide the scallop and sauce mixture between 6 scallop shells or small ovenproof serving dishes.
Mix the bread crumbs, melted butter, andGruyere cheese; divide and spoon the mixture evenly over each dish of scallops. Place the dishes about 5-6 inches from the broiler and cook until the scallop mixture is hot, bubbly, and browned on top. Sprinkle withlemon juiceand serve immediately.
Serve the Coquilles as a first course but it also works very well for a light lunch with a light green salad on the side.