Heat a generous glug of olive oil in a medium saucepan on a medium heat. Peel and slice onion and add to the pot with a pinch of salt to help the onion soften. Cook covered, stirring occasionally for 10 minutes or until onions are soft.

Add spinach and stock and simmer for a few minutes. Taste and season with extra salt if needed, remembering the feta is going to bring a lot of salt.

Divide hot soup between two bowls and top with feta and nuts.