Place the kale into a medium sized frying pan which has a lid. Add a splash of water to the pan with the kale and place the lid securely. Cook over a low-medium heat for 2-3 mins. After 2-3 mins, remove the lid and continue cooking for a minute or just until all of the excess water has evaporated.
Next, slowly pour the whisked egg evenly across the base of the pan, tilt the pan to ensure even coverage.
Then, sprinkle in the frozen peas, spring onions and dot the tomatoes at equal distance across the omelette. Replace the lid and cook over a low-medium heat for about 4-5mins or until the egg is cooked through. Do not be tempted to turn up the heat as this will burn the eggs on the underside.
As soon as the eggs are cooked, serve the omelette while still warm. Season with salt & pepper and add a splash of balsamic vinegar if desired.