Cook peas as directed on package. Drain; keep warm.
Meanwhile, in medium saucepan, combine water, butter and sauce mix; stir to mix. Bring to a boil. Boil 1 minute, stirring constantly. Add milk. Remove from heat. Add potato flakes; with fork, beat well until potatoes are of desired consistency.*
In ungreased 9x5-inch (1 1/2-quart) glass baking dish or 1 1/2-quart microwave-safe casserole, layer half of potatoes. Top with peas, Parmesan and Romano cheese blend and remaining half of potatoes. Sprinkle with Cheddar cheese. Microwave on HIGH for 2 to 4 minutes or until cheese is melted.