Heat the oil in a non-stick pan over medium heat. Add the chicken sausage and sauté to brown (about 2-4 minutes).
Add the tomatoes and eggs. After the egg begins to set around edges, at about 30 seconds, carefully lift the egg from the side with a heat-safe spatula and tilt the skillet. This allows uncooked egg to reach the bottom of the pan. Repeat this process, tilting as necessary.
Add the cheese and avocado; fold the omelet in half to melt the cheese.
Lightly toast the bread and then portion the eggs onto the bread.