Preheat the oven to 350°F (175°C) and grease a 9×13-inch casserole dish with avocado oil or butter. While it heats, chop the onion, green bell pepper, and sweet potatoes into bite-sized cubes.

Heat avocado oil in a Dutch oven or skillet over medium heat. Add onion, bell pepper, and sweet potatoes; cook 8–9 minutes, stirring occasionally, until softened and lightly golden. Stir in minced garlic for the last minute, then transfer everything to the prepared dish.

In the same pan, cook turkey sausage over medium heat, breaking it up as it browns. Drain excess grease and spread the sausage evenly over the vegetables, stirring gently to combine.

Whisk eggs, milk, dried thyme, salt, pepper, and mozzarella in a bowl until smooth. Pour the mixture over the sausage and vegetables, stirring lightly to coat. Bake for 40–45 minutes, or until the center is firm and the top golden. If it browns too quickly, cover loosely with foil.

Let the casserole cool for 15 minutes before slicing. Serve warm and enjoy the comforting blend of savory sausage, tender sweet potatoes, and creamy eggs.