Bring the water to the boil in a lidded large frying pan over high heat. Add the pasta, tomato, rind, oil and salt. Cover; return to the boil. As soon as it comes to the boil, uncover and cook over high heat for 8 minutes, turning the pasta regularly with a pair of tongs to stop the pasta sticking to the base of the frying pan.
Meanwhile, combine capers, olives and extra oil in a small bowl.
Remove pan from the heat. Add spinach and half the parmesan; toss gently with tongs. Season to taste with salt and freshly ground black pepper.
Top with the caper mixture and the remaining parmesan. Serve immediately.