In a large bowl, dissolve the yeast in the water. Let stand until foamy, about 5 minutes.
Using a wooden spoon, mix together 2 cups of the flour, the salt and 2 tablespoons olive oil to make a soft dough. Turn the dough out onto a lightly floured work surface and knead, adding more flour as needed, until soft, smooth and slightly sticky, about 10 minutes.
Form the dough into a ball, transfer to a lightly oiled bowl, turn to coat with the oil, then cover the bowl with a damp kitchen towel or plastic wrap. Let the dough rise in a warm, draft-free spot until doubled, about 1 hour.
Punch down the dough and turn onto a lightly floured work surface. Knead the halved grapes into the dough. Transfer the dough to a lightly oiled baking sheet. Using your fingers, stretch the dough to make a roughly 10-inch oval. Cover the dough loosely with a clean kitchen towel and let it rise in a warm, draft-free place until doubled in bulk, about 1 hour.
In the meantime, preheat the oven to 400° F.
Once the dough has doubled in bulk, brush with olive oil and sprinkle with the coarse sea salt. Place in the preheated oven and bake until lightly browned, about 35 to 45 minutes.
Transfer to a wire rack and let cool in the pan for 5 to 10 minutes. Cut into wedges and serve warm.