Heat oil in a nonstick pan on medium heat. Add, diced onion, sausage, and kale. Cook until the sausage is no longer pink, breaking it up into finer pieces with a spatula.
Pour the eggs into the pan. As the eggs set around the edge of the pan, with a spatula, gently lift the egg to allow uncooked egg to flow underneath. When eggs are almost set on the surface but still look moist, add the cheese. Slip the spatula under the omelet and fold over.
Lightly toast the bread.
Place the eggs on the bread and cut in half. Serve with cantaloupe.