How to Make It
Light a grill. Season the ground beef with salt and pepper and form into eight 4-inch patties that are slightly thicker in the center. Top 4 of the patties with a slice of Brie and a scant tablespoon of the scallion paste. Top with the 4 remaining patties, pinching the edges to seal.
Brush the burgers with oil and grill over high heat, turning once or twice, about 8 minutes for medium-rare meat.
Meanwhile, mix the mayonnaise with the remaining scallion paste. Grill the buns until toasted. Spread the mayonnaise on the bottoms of the buns and top with the burgers, tomatoes and lettuce. Close the burgers and serve.