Season the fish well inside and out and lightly salt the potatoes.
Place the onions, potatoes, tomatoes, garlic and bay leaves in a large mixing bowl. Pour on half the olive oil, season well with salt and pepper and carefully toss together.
Stuff the parsley stalks, lemon and fennel inside the cavity of each fish.
Cover the bottom of a large roomy roasting tray with half the vegetable mixture and spread out in a single layer. Place the bream on top and cover with the remaining vegetables. Drizzle on the remaining olive oil.
Place in the middle of the hot oven and roast for 35 minutes or until the fish is cooked. Serve with lemon and chopped parsley on top, with a salad.