Dice the turkey sausage into small bite-sized pieces.
Heat a non-stick skillet over medium-high heat and add half of the avocado oil.
Add the turkey sausage to the pan and sauté until browned and cooked through, then remove and set aside.
In the same pan, add the spinach and sauté for 1 minute until just wilted, then remove and set aside with the sausage.
Wipe the skillet clean and add the remaining avocado oil, ensuring it coats the bottom of the pan.
Pour the egg whites into the hot skillet and let them sit undisturbed for 2-3 minutes until the edges are golden and crispy.
Place the cooked sausage, spinach, and feta cheese onto one half of the egg whites.
Carefully fold the other half of the omelette over the filling and cook for another minute until the cheese is slightly softened.
Slide the omelette onto a plate and serve immediately with fresh sliced avocado on top.