1. Combine rapid-rise yeast, warm water, and sugar in a small bowl, and let stand 5 minutes or until mixture bubbles.
2. Stir together 2 cups flour and next 3 ingredients in a large bowl; stir in yeast mixture and 2 Tbsp. oil until well blended (dough will be sticky). Turn dough out onto a well-floured surface, and knead until smooth and elastic (about 3 to 5 minutes). Place in a well-greased bowl, turning to grease top. Cover with plastic wrap, and let stand 15 minutes.
3. Sprinkle cornmeal onto a baking sheet. Place dough on baking sheet, and roll into a 12-inch square, sprinkling with flour as needed to prevent sticking (about 1 Tbsp.). Cover with plastic wrap, and let rise in a warm place (85°), free from drafts, 45 minutes.
4. Preheat oven to 400°. Brush dough with balsamic vinegar. Gently press end of a wooden spoon into top of dough, forming indentations. Top with tomatoes and cheese. Sprinkle with salt and pepper. Drizzle with remaining 1 Tbsp. oil.
5. Bake at 400° for 20 minutes or until golden and cheese is melted. Cool 5 minutes, and cut into squares.