Wash your hands well with soap and warm water for at least 20 seconds.
Coat 9 x 13 baking dish with vegetable oil cooking spray.
Add frozen hash browns to baking dish.
Buy pre-washed or fresh spinach. If using fresh, then remove stems and place leaves in a bowl of water for about a minute. Drain in a colander and then pat leaves dry with paper towels. Chop spinach leaves and add to baking dish.
Wash bell pepper and cut into small pieces. Add to baking dish.
Peel onion and cut into small pieces. Add to baking dish.
Crack eggs into a mixing bowl. Add yogurt, mustard, and salt and stir with a fork or whisk until mixture is smooth. Add egg mixture to baking dish.
Add cheese to baking dish and mix all ingredients until well coated in the egg mixture.