Preheat oven to 450ºF. Spread grapes onto a sheet pan. Drizzle with olive oil. Sprinkle with salt. Lay thyme leaves over top. Toss all together gently with your hands. Place pan in the oven for 7 to 9 minutes or until grapes just begin to burst.
Mix the Boursin cheese with enough cream to make it slightly soft and runny, set aside.
Meanwhile, heat a grill or grill pan to medium-high. Brush the bread with olive oil. Grill until nice and toasty.
Assemble the open-faced sandwiches: Spread Boursin mix over bread. Top with roasted grapes. Discard thyme sprigs.