Preheat the oven to 375F. Then, grease a 9x13 inch casserole dish and set aside.
Next, heat a large skillet over medium-high heat. Once hot, add the oil and sausage. Cook until brown, breaking it up as it cooks.
Once the sausage is brown, add the chopped onion and bell peppers. Sauté for about 5-7 minutes or until onion and bell pepper start to become tender. Add the garlic and red pepper flakes and cook for another 1 minute.
Next, add the baby spinach to the skillet, sauté for about 30 seconds or until the spinach is wilted, and then remove from the heat. Set aside and let cool.
Next, in a large mixing bowl, add the eggs, half and half, green onion, hot sauce, salt, pepper, Italian seasoning, and chopped parsley. Whisk together until well combined and then mix in the shredded cheddar cheese.
In the prepared casserole dish, add the sausage mixture and potatoes. Then, evenly pour the egg mixture over the sausage, veggies, and potatoes. Add additional shredded cheese to the top, if desired.
Then, bake the casserole at 375 degrees for 40-50 minutes or until the egg is completely set. Let cool and then slice into 12 squares. Top with sour cream and green onion and enjoy!