Finely chop the onion. Cut the pepper into 2cm cubes.
Put 1 Tbsp oil in a large pan, add the onion and pepper, the sauté under a lid until tender.
Meanwhile put the anchovies, capers, garlic, parsley, dill and the lemon juice into a small food processor and blend until you get a textured paste. Add the remaining oil and lemon zest to this paste. Set aside.
When the vegetables are soft, add the prawns, put the lid on and cook for 3-5 minutes until they change colour (or warm through if pre-cooked prawns used).
Cook the pasta according to the pack instructions, then drain. Add the pasta to the prawns, together with the anchovy pesto, and toss well.
Season with salt & the pepper. Serve warm.