Heat a non-stick skillet over medium heat and lightly brown the turkey sausage links until cooked through.
Slice the sausage into rounds and set aside.
In the same pan, toss the fresh baby spinach until just wilted, then remove and set aside with the sausage.
Wipe the skillet and add the olive oil, ensuring the surface is well-coated.
Pour the whisked egg whites into the pan, cooking undisturbed until the edges begin to set.
Carefully lift the edges of the omelet to let the uncooked egg flow underneath.
Once the center is mostly set, arrange the sausage, spinach, and crumbled feta over one half of the omelet.
Fold the omelet over the filling and slide it onto a plate.
Top with fresh avocado slices and a pinch of black pepper for a creamy finish.