Preheat oven to 350°F (175°C) and grease a 9x13 inch casserole dish.
Heat avocado oil in a Dutch oven or large saucepan over medium heat.
Add onion, green bell pepper, and sweet potatoes; cook 8-9 minutes, stirring occasionally until vegetables soften.
Add minced garlic during the last 1-2 minutes of cooking, then remove vegetables from heat.
Spread cooked vegetables evenly in the prepared casserole dish.
In the same pan, cook the turkey sausage until fully browned, breaking into small pieces.
Combine cooked sausage with vegetables in the casserole dish and stir well.
In a mixing bowl, whisk together eggs, milk, mozzarella cheese, salt, dried thyme, and pepper.
Pour the egg mixture over the sausage and vegetables, stirring gently to distribute evenly.
Bake uncovered for 40-45 minutes or until the center is set; cover with foil if top browns too quickly.
Remove from oven and let cool for 15 minutes before serving.