Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Peel the sweet potato and cut into 1/2-inch cubes, then toss them on the baking sheet with 1 tablespoon of olive oil and a pinch of sea salt.
Roast the sweet potatoes for 20-25 minutes, flipping halfway through, until they are tender and the edges are golden brown.
While the potatoes roast, heat the remaining 1 tablespoon of olive oil in a non-stick skillet over medium heat.
Dice the turkey sausage and red onion, then add them to the skillet and sauté until the sausage is browned and onions are soft.
Add the fresh spinach to the skillet and cook for 1 minute until just wilted, then remove the mixture from the pan and set aside.
Wipe the skillet clean and pour in the egg whites, cooking over medium-low heat until the bottom is set and the top is almost firm.
Spread the sausage and spinach mixture over one half of the omelet, then carefully fold the other half over the filling.
Slide the omelet onto a plate and serve immediately alongside the roasted sweet potatoes.