1. Heat a Dutch oven over medium heat. Add oil to pan, swirling to coat. Add shallots and garlic to pan; cook 2 minutes or until tender, stirring frequently. Stir in coconut milk and next 7 ingredients (through Sriracha); bring to a boil. Add mussels to pan; cover and cook 5 minutes or until shells open. Discard any unopened shells.
2. Remove mussels from pan with a slotted spoon, reserving broth mixture. Divide mussels between 2 serving bowls; keep warm. Bring broth mixture to a boil; cook 5 minutes. Pour 1 cup sauce over each bowl. Sprinkle with sliced basil, if desired.
Scallion rice: Combine 1 cup water, 1/2 cup jasmine rice, 1 teaspoon butter, 1/4 teaspoon kosher salt, and 1 thinly sliced green onion in a small saucepan; bring to a boil. Cover, reduce heat, and simmer 15 minutes; remove from heat. Let stand 5 minutes. Fluff with a fork.