Preheat the oven to 350 degrees F (175 degrees C). Grease an 8x11-inch casserole dish with cooking spray.

Mix hash browns, eggs, ham, Cheddar-Jack cheese, onion powder, salt, and pepper together. Pour mixture into the prepared dish. Shake dish gently from side to side to level out ingredients.

Bake, uncovered, in the preheated oven until top starts to brown, about 40 minutes. Cool before cutting into bars.