Toss the grapes with the red wine, thyme, 1 tablespoon of the olive oil and some salt and pepper. Place on a small baking sheet or baking dish. Roast until the grapes are tender, wilted and juicy, about 25 minutes.
Heat a grill pan over medium-high heat. Brush the bread slices with the remaining tablespoon of olive oil. Grill on both sides until crisp and lightly charred in some places, 3 to 4 minutes per side. Spread the ricotta evenly on the bread. Top with the roasted grapes and their juices. Sprinkle with lemon zest and flaky salt, then serve.