In a small bowl, whisk the mayonnaise with the lemon juice and gradually whisk in the remaining the olive oil and season with salt and pepper.
Take the beef and season well with salt, pepper and the herbs de Provence mix well and shape into eight balls. Flatten each ball out in the palm of your hand and place a slice of brie in the centre. Close the meat round the cheese and seal into a burger shape. Cut the bacon strips in half and place the bacon on the grill. Place the burger on the grill for 5 minutes, turning once. Do not worry if a little cheese seeps out, its fine. During this cooking time split the brioche buns and place them cut side down on the griddle to warm.
When everything is ready, spread the lemon mayonnaise on the cut sides of the buns; set the burgers on the bottoms and top with the bacon and top bun.