For the marinade: In a small bowl, combine the orange juice, lemon juice, green onions, garlic, olive oil and red pepper flakes.
For the fish packets: Cut four 12-by-17-inch pieces of aluminum foil; place one piece of fish in the center of each. Sprinkle the fish with salt and pepper. Divide the marinade evenly among the packets (about 1/2 cup for each).
In a large bowl, toss the string beans, mushrooms, onions and tomatoes with the olive oil. Season the vegetables with salt and pepper, then divide evenly among the packets. For each packet, fold the foil over at the top to close, and then close up the sides to seal completely. Chill in the refrigerator for 30 minutes before cooking, to give the fish time to marinate.
Preheat the oven to 400 degrees F.
Transfer the packets to a baking sheet. Bake until the fish flakes, 12 to 15 minutes. Serve immediately.