Boil the eggs in a pan of salted water for 10 minutes. While the eggs are cooking, steam the chopped spinach leaves gently for 4-5 minutes.
Cover the eggs in cold water for one minute to cool, then peel. Place the eggs in a bowl and add the butter. Season with salt and pepper and mash thoroughly with a fork.
Serve the thickly onto the oatcakes. Serve with the spinach and tomatoes.