Preheat your oven to 375°F (190°C). In a large skillet, heat the olive oil over medium-high heat. Add the ground breakfast sausage and cook, breaking it up with a spoon, until it's browned and cooked through, about 5-7 minutes. Drain any excess grease. If using chopped onion, add it to the skillet with the sausage for the last 3-4 minutes of cooking until softened.
If using baby spinach, add it to the skillet with the cooked sausage and onions. Cook for an additional 1-2 minutes until the spinach wilts. Evenly spread this sausage and vegetable mixture into a 9x13 inch oven-safe baking dish.
In a large mixing bowl, whisk together the large eggs, heavy cream (or unsweetened almond milk), garlic powder, salt, and black pepper until all ingredients are well combined and frothy.
Pour the whisked egg mixture evenly over the sausage and vegetables in the baking dish. Sprinkle the shredded cheddar cheese evenly over the top of the egg mixture.
Bake in the preheated oven for 25-30 minutes, or until the eggs are completely set in the center and the top is lightly golden brown. Let the bake stand for 5 minutes before slicing and serving.
Notes
This bake is excellent for meal prepping! Store individual portions in airtight containers in the refrigerator for up to 4 days. Reheat gently in the microwave or oven. For a spicier kick, add a pinch of red pepper flakes with the seasonings.