Heat a large saucepan over medium heat. Add oil; swirl to coat. Add oregano, pepper, and garlic; sauté 30 seconds. Add wine; cook 1 minute. Add broth and water to pan; bring to a boil. Stir in orzo; cook 6 minutes or until al dente.
Stir in marinara, shrimp (if using), and red pepper; cook 4 minutes or until shrimp turn pink and cooked through. Place soup in each of 4 bowls, and top each serving with chopped oregano.