Whisk the egg whites in a large bowl. Chop the tomatoes into small cubes. Trim the spring onions and thinly slice diagonally. Remove any hard stalks from the dill and finely chop.
Put the oil in a frying pan and warm over a medium to high heat. Add the tomatoes and spring onions and cook for 3 minutes, stirring occasionally. Reduce to a medium heat, then add the eggs, dill and seasoning and allow to cook for 2-3 minutes, stirring constantly until the eggs are almost cooked. Remove from the heat and continue to stir, as the eggs will keep cooking. Most of the moisture should have disappeared, but the mixture should still be moist.
Meanwhile, toast and butter the toasted rye bread. Cover with the scrambled egg to serve.