Preheat oven to 350 degrees. Spray a large baking dish with cooking spray.
Heat olive oil in a large skillet over medium-high heat. Add the green pepper and onion and saute until they begin to soften and the onion is translucent, 7-8 minutes. Add the garlic and cook 1 minute more. Add the vegetables to the baking dish.
Add the chopped spinach, hashbrowns, and 1 cup cheddar cheese. Stir gently to combine.
In a medium bowl, whisk together the eggs, salt, pepper, mustard, and yogurt. Pour evenly over the hashbrowns mixture. Top with remaining cheese.
Bake for 45-50 minutes until golden brown and the eggs are set.
