Preheat the oven to 375°F (190°C) and grease a casserole dish.
In a large mixing bowl, whisk together the eggs and heavy cream until well combined. Add in the shredded cheddar cheese, diced red bell pepper, diced yellow onion, chopped fresh parsley, salt, and black pepper. Mix everything together until well combined.
Heat the olive oil in a skillet over medium-high heat. Once hot, sauté the diced bell pepper and onion until slightly softened.
Transfer the sautéed vegetables to the prepared casserole dish. Pour the egg mixture over the vegetables and gently stir to distribute evenly.
Bake in the preheated oven for about 20-25 minutes or until the eggs are set and the top is golden brown.
Remove from the oven and let it cool for a few minutes before serving.
Slice into portions and enjoy your delicious Keto Baked Egg Casserole!