Preheat the oven to 350°F (175°C).

In a large skillet, cook the breakfast sausage over medium-high heat until browned and crumbly, about 5-7 minutes. Transfer to a bowl and set aside.

In a separate bowl, combine Cheddar and mozzarella cheeses. Set aside.

Cut the tops off the bell peppers and remove seeds and veins. Parboil in boiling water for 4-5 minutes, then rinse with cold water. Dry and season the inside with salt and pepper.

In the same skillet, heat olive oil over medium-high heat. Add frozen shredded potatoes and diced onion. Cook until the potatoes are golden and crispy, about 5-7 minutes.

Add cooked sausage, half of the cheese mixture, beaten eggs, salt, and black pepper. Turn off the heat and stir gently. Let sit for 5 minutes.

Stuff the peppers about 90% full, leaving room for the reserved cheese. Place in a broiler-safe baking dish, cover with foil.

Bake for 15 minutes, uncover, and bake for another 10 minutes until eggs are set and peppers are tender.

Sprinkle reserved cheese on top and broil for 4-5 minutes until bubbly and browned.