In a large saucepan combine oil, ginger, and crushed red pepper. Cook and stir over medium heat 2 minutes. Add broth; bring to boiling. Stir in rice; reduce heat. Simmer, covered, 15 to 20 minutes or until rice is tender.
Tear lime leaves in several places from the edges toward the centers (if using). Cut lemongrass into 1-inch pieces; bruise with the flat side of a knife. Add lime leaves and lemongrass to rice mixture. Stir in the next seven ingredients (through snipped cilantro). Bring to boiling; reduce heat. Simmer, uncovered, 5 minutes.
Discard lime leaves (if using) and lemongrass. Stir lime juice into soup. Serve immediately. If desired, serve with green onions, cilantro sprigs, and lime wedges.