To make the dressing put the olive oil, sugar, lemon zest and juice into a bowl and mix well. Finely chop half of the mint and add it to the bowl, then season to taste. Whisk until slightly thickened.
Bring a large pan of water to the boil. Trim off any tough ends from the broccoli, then blanch it in the boiling water for 2mins. Drain well. Put it in a bowl and pour over half of the dressing. Toss together to coat all the stems.
Remove the remaining mint leaves from their stems. Crumble the feta over the broccoli, then scatter over the chilli and the mint leaves.
Pour over the remaining dressing and serve.