Heat the oil in a large frying pan on a medium temperature. Once warm add the fennel seeds and gently toast them making sure they don’t burn.
Dice the onion and crush the garlic. Add them to the toasted fennel seeds.
Once the onion has started to caramelise, finely chop the tomatoes and then also add them to the pan, followed by all of the zest and half the juice of the lemon, a pinch of salt, some black pepper and a sprinkle of chilli flakes. Leave to simmer and add a dash of boiling water if you need to stop it sticking.
Bring the pasta to boil and add the kalettes 3-5mins from the end.
Strain most the water off the pasta and kalettes once cooked. Add the pasta, kalettes and a little of the leftover cooking water to the frying pan with the sauce. Flake in the sardines, and toss around until all coated.
Serve with a squeeze of lemon juice and a couple of olives.