Preheat oven to 425°F and line a baking sheet with a large piece of foil; fold in sides slightly to form a rim. Place grapes on foil and top with wine, vinegar, olive oil, and sea salt. Stir lightly to coat grapes with mixture. Roast for 30 minutes, stirring every 10 minutes. Remove grapes with a slotted spoon and cook juices for 8 to 10 minutes more or until thickened, making sure to not burn. (Swirling the pan occasionally helps to cook evenly.) Let cool slightly, then pour over roasted grapes. Top each baguette slice with about 2 rounded teaspoons of ricotta cheese. Top with grapes and a bit of the juices. Grate lemon zest over the top.