Preheat the oven to 200°F. (If making multiple omelettes, keep the cooked omelets in the oven on a baking sheet until all are complete.)
In a non-stick pan, heat olive oil over medium heat. Sauté spinach until wilted, then add in the tomatoes and egg.
After egg mixture begins to set around edges, at about 25-30 seconds, carefully lift the egg from the side with a heat-safe spatula and tilt the skillet. This allows uncooked egg to reach bottom of skillet. Repeat this process, tilting as necessary.
In a non-stick pan over medium heat, brown the chicken sausage on both sides. Then toast the bread.
Add feta cheese and fold the omelet in half with a spatula.
Portion and serve with toast, chicken sausage, and apples.