Thaw shrimp, if frozen. Peel and devein shrimp. Cut tails off shrimp. Rinse shrimp; pat dry with paper towels. Set aside. Cut green onions into 1/2-inch slices, keeping white parts separate from green tops. Set green tops aside. In a large saucepan heat oil over medium heat. Add white parts of the green onions and the sweet peppers; cook for 5 minutes, stirring occasionally. Add ginger and garlic; cook and stir for 1 minute more.
Add the water, broccoli, soy sauce, and crushed red pepper. Bring to boiling; reduce heat. Simmer, uncovered, for 2 minutes.
Add shrimp and kale (if using). Return to boiling; reduce heat. Simmer, uncovered, for 2 to 3 minutes or until shrimp are opaque. Stir spinach (if using), green onion tops, lemon peel, lemon juice, and sesame oil into hot soup just before serving. If desired, sprinkle with sesame seeds.