Wash hands with soap and water.

Preheat oven to 425 °F.

Wash your hands and work area.

In large bowl, combine hash browns, green pepper, 1/4 cup onion, salt, and 1/4 teaspoon pepper.

Spray a 8x8 inch baking dish with non-stick cooking spray. Press potato mixture into bottom.

Bake until lightly browned around edges, 20 to 25 minutes.

In large bowl, stir together evaporated milk, egg whites, 1/4 teaspoon pepper, cheeses, spinach, remaining 1/4 cup onion, and tomatoes.

Reduce oven temperature to 350 °F.

Pour mixture over potato crust. Bake uncovered until center is set, 40 to 45 minutes.