Combine marinade ingredients in a bowl.
Pour marinade into resealable plastic bag.
Add flounder fillets and seal bag securely.
Turn bag several times so all surfaces of fish are coated by marinade.
Refrigerate and marinate for 1 hour, turning once.
Drain and discard marinade.
Preheat stovetop grill.
Cook flounder over medium-high heat about 4 to 5 minutes, turning once.
Remove flounder to serving dish.