Heat half of the oil in a small frying pan. Add the capers and fry until crispy, for about 3 minutes. Turn off the heat.
Put the sardines into a bowl. You can break them up with a fork into small chunks, if preferred. Add the chopped parsley, lemon juice and zest lemon zest, then the capers with their cooking oil. Toss very gently.
Lightly toast the sourdough slices and put them on two plates.
Meanwhile, cut the tomatoes in half. Add the remaining olive oil to the pan and fry the tomatoes for a couple of minutes, then transfer them to the plates.
Add more oil to the pan, if needed, then crack the eggs into it (if you want fried eggs) and fry the eggs until they are done to your liking. Alternatively, crack the eggs into a small bowl, add a pinch of salt and whisk until light and fluffy, then fry in pan, stirring, until you get scrambled eggs.
Add the fried or scrambled eggs to the plates, then top with the sardine mixture.
Serve warm.