This Thai stew doesn't simmer for hours -- coconut milk gives instant flavor and shrimp cook in mere minutes.
Cook rice according to package instructions; set aside, covered. Meanwhile, place cornstarch in a medium bowl. Gradually whisk in coconut milk, sugar, and 1 cup water; set aside.
In a large skillet, heat oil over medium. Add bell peppers, onion, garlic, ginger, red-pepper flakes, and scallion whites; season with salt. Cook, tossing frequently, until vegetables are crisp-tender, 6 to 8 minutes.
Add coconut-milk mixture to skillet; raise heat to medium-high. Boil, stirring occasionally, until thickened, 1 to 2 minutes. Add shrimp, and cook just until opaque, 3 to 4 minutes. If necessary, adjust consistency of stew with a little bit of water; season with vinegar and salt to taste.
Fluff rice gently with a fork. Serve shrimp stew over rice, garnished with scallion greens.
Sharp, fragrant ginger invigorates this dish. Because it's potent and fibrous, use a sharp knife to mince it. To keep this stew tasting bright, avoid overcooking the vegetables.