Cook garlic in oil in a deep 4 to 6 quart heavy pot over moderately low heat, stirring, until garlic is fragrant, about 1 minute.
Stir in tomatoes and 1 tablespoon oregano and cook, stirring occasionally, until tomatoes break down, 4 to 5 minutes. Season with pepper.
Add clams, stirring well to coat, then cover pot tightly and increase heat to moderately high. Cook, stirring once, until clams open, 5 to 7 minutes. (Discard any clams that have not opened after 7 minutes.)
While clams are cooking, toss together bread crumbs, zest, and remaining tablespoon oregano. Divide clams and pan juices among clam shells, then sprinkle with bread crumbs. Serve immediately. Serves 8.
Note: Larger hard-shelled clams such as littlenecks (2 to 2 1/2 inches in diameter) can be used, but cooking time will increase to 8 to 10 minutes.