Combine first 4 ingredients in a 12-inch, straight-sided skillet; bring to a boil. Reduce heat to medium-low or until mixture simmers. Add scallops; cover and poach at a light simmer, adjusting heat as necessary, for 8 minutes or until scallops turn opaque.
Using a slotted spoon, remove scallops from skillet; place in a shallow dish or individual serving bowls. Cover with foil. Boil coconut-milk mixture over high heat, uncovered, for 10 to 15 minutes or until reduced to 1 1/2cups. Stir in fish sauce and basil; spoon over scallops.