Preheat the oven to 200 degrees. (if making multiple omelets keep cooked omelets in the oven on a baking sheet until all are complete)
In a medium bowl, whisk together eggs, salt, and black pepper.
In a nonstick pan over medium heat. Brown the ground sausage, breaking it up into smaller pieces with a spatula. (There should be enough fat in the pan from the sausage, if not you can add a drizzle of olive oil)
Add in the eggs. After the eggs begin to set around edges, about 1 minute, using a spatula, carefully lift the egg from the side, and tilt the pan so uncooked egg can reach the bottom of the pan. Repeat this process, tilting as necessary until the eggs are no longer runny.
Toast the bread.
Add the feta cheese, tomato, and avocado; fold the omelet in half and set on a plate. Serve with toast and orange sections.