Put the lemon juice and zest into a
large bowl, tip in the onion, then season
with salt and pepper. Set aside for
10 mins, to let the onion soften a little.
Boil the spaghetti for 10 mins. Mix
the oil, capers, chilli and sugar into the
lemony onions, then season generously.
When the pasta is ready, drain, toss
with a splash of oil, then let cool awhile.
Put into the bowl with the dressing, tip
in the tomatoes and most of the herbs,
then toss well. Tear in the mozzarella and
toss ever so gently. Put into bowls, top
with more herbs and drizzle with more
oil to serve.