Heat the oven to 230C/450F/gas mark 8. Toss the courgettes in a bowl with the oil and fennel seeds, and season generously. Spread out on an oven tray and roast for 15-20 minutes, until they’re tender and blistering slightly.
Remove from the oven and leave to cool. If you have courgette flowers, remove the stigmas and stamens, then open them out like butterflies.
Melt the butter in a large, nonstick frying pan over a medium heat, then gently fry the spring onions for a couple of minutes, until softened. Beat the eggs in a bowl, mix in the mint and chives, then season well and pour into the softened onions.
Cook for a minute or so, until you can see the bottom begin to turn opaque, then scatter the roast courgette pieces. If you are using courgette flowers, layer these on top of the roast courgettes, then lay the cheese on last.
Keep cooking the frittata until the base and edges are done, and just the middle remains loose and uncooked. Transfer the pan to a hot grill and cook until the centre is solid and the cheese has melted.
Once the frittata is ready, leave it to stand for five minutes, then run a knife around the edge, loosen the bottom gently with a spatula, then slide it on to a plate. Scatter with some mint leaves and chives, and serve warm or at room temperature.