Using slotted spoon, transfer to a plate. Add remaining vegetable oil to skillet. Add vegetables; stir-fry until crisp-tender, about 3 to 4 minutes. Add garlic and ginger; stir-fry 30 seconds.
Drizzle reserved marinade mixture over vegetables. Stir-fry until marinade thickens slightly, about 30 seconds.
Toss in reserved clams. Season to taste with pepper. Transfer to bowl. Sprinkle with scallions and serve with rice.