Cook the pasta according to the packet instructions.
Meanwhile, peel one avocado and mash it with a fork or whiz it in a small food processor.
Mix in the pesto, season, add some lemon juice and set aside.
Thinly slice the onion and garlic and cut the tomatoes in half.
Heat the oil in a small frying pan then gently sauté the onion for 8 minutes or until soft. Add the balsamic vinegar and caramelise it then transfer to a plate.
Add the garlic and the tomatoes to the pan and some more balsamic vinegar and a drop of oil. Quickly fry them, cut side facing downwards, until they are slightly charred. Add a drop of the pasta’s cooking water too.
When the pasta is cooked, drain then mix with the pesto.
Add the caramelized onion and tomatoes, then toss gently.
Cut the avocado in half, take out the stone, then remove the skin. Slice or cube the flesh and add these to the pasta together with the chopped herbs.
Serve with a squeeze of lemon or lime juice.