Season the tomatoes with pepper. Heat a pan sprayed with cooking spray oil over a medium heat, add the tomatoes and cook for 2-3 minutes, until softened, stirring from time to time but not breaking up the tomatoes.
Meanwhile, beat the eggs in a bowl with some pepper. Stir in the salmon and chives and pour into a saucepan.
Cook very gently for 3-4 minutes, stirring slowly, until the eggs are softly scrambled. Remove from the heat and stir for a few seconds.
Divide the tomatoes between two plates and serve with the scrambled eggs and watercress.