Preheat oven to 425 degrees F (220 degrees C). Lightly oil a shallow, 2 quart baking dish.
In a medium bowl, toss the potatoes with 2 tablespoons olive oil to coat evenly. Season with salt and pepper. Spread potatoes in baking dish with 1/4 cup water. Cover, and bake for 15 minutes.
Combine bell peppers, leek, zucchini, and celery in a medium bowl. Toss with garlic and 2 tablespoons olive oil,. Season to taste with salt and pepper. Spread vegetables over potatoes, add another 1/4 cup water, and cover. Bake for 10 to 15 minutes.
Rinse, and cut fish into 1 to 1 1/2 inch cubes, and spread over vegetables. Cover. Bake for 10 minutes, or until fish flakes easily. Serve with tomato and parsley or fennel garnish.