Cut sugar snap peas on the diagonal into about 1/2-inch lengths. Cut scallops in half to form half-moon shapes.
In a small bowl or glass measure, whisk chicken broth, mirin, and cornstarch until well blended.
Pour oil into a 12-inch nonstick frying pan or 14-inch wok over high heat. When hot, stir in green onions, garlic, and chile flakes. Stir until fragrant, 30 to 45 seconds.
Add scallops and cook, stirring occasionally, until surface of scallops is mostly opaque, about 2 minutes. Stir in sugar snap peas, and pour in broth mixture. Cook, stirring, until sauce is thick and glossy and scallops are opaque but still moist-looking in center of thickest part (cut to test), 2 to 3 minutes.
Stir in half the basil, then pour into a serving bowl and sprinkle with remaining basil.
Serve with cooked rice.