In a medium nonstick skillet, combine onion slices, olive oil, salt, and sugar. Cover and cook over low heat about 10 minutes or until onion is tender. Using a mortar and pestle, grind coriander, fennel, and pepper to a coarse powder.
Meanwhile, preheat oven to 500 degree F. Cut dough into 6 to 8 equal pieces. Sprinkle each piece with 1/4 teaspoon of the spice mixture. Knead until well combined. Cover and let stand for 10 to 15 minutes.
Place pizza stone or a heavy baking sheet in the 500 degree F oven. Heat stone or baking sheet for 10 minutes.
Sprinkle work surface with cornmeal. Shape or roll dough into round disks, each approximately 4 to 5 inches in diameter. Divide the onion mixture among rounds; arrange rounds on hot pizza stone or baking sheet.
Bake for 7 to 9 minutes or until the rounds are golden brown. Serve warm. Makes 6 to 8 servings.
You can prepare the seasoned dough several hours ahead of serving. Place shaped rounds on a baking sheet; cover with plastic wrap. Refrigerate and allow to come to room temperature before baking.