Place the oil in a large, deep skillet and turn the heat to medium. Add the onion, garlic, ginger, and chilies and cook, stirring frequently, until the vegetables are tender and the mixture pasty. Stir in curry powder and coconut milk, and lime juice and simmer, stirring occasionally, until thickened, 5 to 8 minutes.
While sauce simmers, season shrimp with salt and pepper. Add shrimp to sauce and simmer, stirring occasionally, until shrimp are just cooked through, about 3 minutes. Add bok choy for the final 2 minutes of cooking time until just barely tender. Add salt to taste and serve immediately with basmati rice and optional garnishes.