Preheat oven to 400°F (200°C). Lightly grease a 9×9-inch (or similar) baking dish and set aside.
On a parchment-lined baking sheet, toss the diced sweet potato with 1 tbsp olive oil, ½ tsp salt, and ¼ tsp pepper.
Spread in a single layer and roast for 15–18 minutes, until just fork-tender and lightly golden at the edges. (They will finish cooking in the casserole.)
While the sweet potatoes roast, heat 1 tsp olive oil in a skillet over medium heat.
Add the ground turkey sausage, breaking it up with a spatula, and cook until browned and cooked through, about 5–7 minutes.
Stir in the red onion and bell pepper and cook another 3–4 minutes, until softened and fragrant.
Add the spinach (or kale) and cook just until wilted, 1–2 minutes. Remove from heat.
In a large mixing bowl, whisk together the eggs, egg whites, cottage cheese, and almond milk until mostly smooth.
Whisk in garlic powder, Italian seasoning, smoked paprika, salt, and pepper.
Reduce oven temperature to 375°F (190°C).
Bake for 20–25 minutes, or until the center is just set and no longer jiggly and the top is lightly golden.
Let rest for 5–10 minutes before slicing.
Garnish with green onions, herbs, or avocado, and serve warm.
