In a medium saucepan cook zucchini, covered, in a small amount of boiling water for 2 to 3 minutes or just until tender. Drain zucchini. Set aside.
Meanwhile, coat six 8- to 10-ounce individual casseroles or ramekins with cooking spray. In a large bowl toss together bread cubes, cheese cubes, and zucchini. Divide equally among prepared casseroles.
In a medium bowl combine eggs, milk, green onions, the 2 tablespoons dill, the salt, and pepper. Pour evenly over mixture in casseroles. Using the back of a large spoon, press bread and cheese pieces down to moisten. Cover with plastic wrap; chill for 4 to 24 hours.
Preheat oven to 325 degrees F. Remove plastic wrap; cover casseroles with foil. Bake for 20 minutes. Uncover and bake for about 20 minutes more or until a knife inserted near the centers comes out clean. Let stand for 10 minutes before serving. If desired, garnish with fresh dill sprigs.