In a bowl mix together the cheese with the butter and diced chives.
Cut a sheet of wax paper approximately 10 x 10 inches. Mold the prepared butter in a strip about 1 1/2 inches wide along the front edge of the paper then roll up tightly , twisting the ends to form a fat bonbon shape. Place in the freezer overnight.
In a large bowl, mix the remaining ingredients, then divide the hamburger mix into 8 evenly sized patties.
Remove the cheese roll from the freezer, allow to soften slightly and cut into 4 equal slices.
Place a slice of cheese roll on 4 of the patties and use the remaining 4 patties as lids; with your fingertips, pinch the edges together to seal in the cheese filling. Brush the burgers with a little oil.
Heat the grill and, when smoking hot, cook the burgers for 4-5 minutes on each side.
To serve, top each section of the baguette with a sliced tomato, then a grilled burger, and top with some dressed salad leaves, and serve.