Preheat oven to 400°F. Toss sweet potato cubes with 1 teaspoon oil and a pinch of salt, spread on a sheet pan, and roast 18 to 20 minutes until tender. Reduce oven to 375°F.
Meanwhile, heat remaining 1 teaspoon oil in a skillet over medium heat. Add chicken sausage and cook 4 to 5 minutes, turning occasionally, until lightly golden.
Add spinach and green onions to the skillet. Sauté 1 to 2 minutes until spinach wilts; remove from heat.
In a large bowl, whisk eggs with remaining salt, garlic powder, and black pepper until fully combined.
Lightly grease a 9x13 nonstick casserole dish. Layer roasted sweet potato, sausage, and the spinach mixture evenly across the bottom.
Pour the egg mixture evenly over the layers and gently shake the dish to settle.
Bake at 375°F for 28 to 32 minutes, until the center is set and a knife inserted in the middle comes out clean.
Cool completely on the counter for at least 20 to 25 minutes before slicing to keep clean edges and prevent moisture buildup.
Slice into 6 equal portions and transfer to glass meal prep containers. Label with the date and refrigerate.