1. Stir together yeast and warm water (100° to 110°) in bowl of a heavy-duty electric stand mixer; let stand 5 minutes. Add bread flour, salt, and 1/4 cup oil to yeast mixture; beat on low speed, using paddle attachment, 25 seconds or until blended. Add chopped herbs. Switch to dough hook; increase speed to medium-high, and beat 5 minutes. (Dough will be sticky.)
2. Place dough in a large, well-greased bowl, turning to coat top. Cover with plastic wrap, and let rise in a warm place (80° to 85°), free from drafts, 1 hour or until doubled in bulk.
3. Drizzle 1/4 cup olive oil in a half-sheet pan or jelly-roll pan; place dough in pan. Press dough down and into edges of pan, using your fingers. (It's okay if there are holes in the dough.) Cover with plastic wrap, and let rise in warm place 1 hour.
4. Preheat oven to 425°. Scatter grapes over dough. Drizzle with remaining 1/4 cup olive oil, and sprinkle with coarse salt and freshly ground black pepper. Bake 30 to 35 minutes or until golden brown. Serve warm or at room temperature.