Evenly coat 8x8x2-inch baking dish with spray. Line bottom of dish with 2 cups bread cubes. Sprinkle with 1/2 cup each of cheese and ham and all peppers and onions. Top with remaining 2 cups bread cubes. Sprinkle with remaining 1/2 cup ham. In medium bowl, beat together eggs, milk and garlic powder until well blended. Pour evenly over layers. Cover with plastic wrap.
Microwave on full power 5 minutes. Rotate dish 1/4 turn. Microwave on 50% power, rotating dish 1/4 turn each 3 to 5 minutes, until thermometer inserted near center reads 160° and/or knife inserted near center comes out clean, about 10 to 12 minutes. Remove plastic wrap. Sprinkle with remaining 1/2 cup cheese.
Note: Microwave cooking times are based on full power output of 1000 to 1100 watts. For an oven with lower wattage, allow more time.