Pour water into a medium sauté pan 1-1/2 inches deep. Bring water to boil over high heat. Add chicken (it should be covered by 1/2-inch water) and reduce heat to medium. Cover and cook for 8 to 10 minutes or until just cooked through. Drain and discard cooking liquid. Transfer chicken to plate. When cool enough to handle, cut into 1-inch pieces.

Stir together croutons, water, and margarine in a medium bowl. Let stand for 4 to 5 minutes or until all the water is absorbed. Pat half of mixture into prepared baking pan.

Lightly beat eggs in a small bowl and whisk in milk. Pour over casserole. Cover baking pan with foil and refrigerate overnight.

Bake, uncovered, for 50 minutes. Sprinkle with cheese and bake for an additional 10 to 20 minutes or until the cheese is melted, begins to bubble, and is light golden brown.