Heat your oven to 180°C/Fan 160°C/Gas 4. Crack the eggs into a large bowl and whisk well. Peel and thinly slice the onion. Add it to the eggs. Halve and deseed the chilli. Finely chop it and add to the bowl.
Finely shred the mint leaves and add half to the eggs (keep the other half for later). Add a pinch or 2 of cayenne, depending on how spicy you like your food (it's hot). Finely grate in the lemon zest. Beat together. Fold in the white crab meat and season well with salt and pepper. Set aside.
Trim the dry ends off the purple sprouting broccoli and halve any thick stalks. Heat a dry, medium frying pan over a medium heat for 1 min. Add the broccoli. Cook for 3-4 mins, turning once or twice, till slightly charred and softened. If the pan isn’t ovenproof, transfer the broccoli to an ovenproof dish.
Pour the chilli crab egg mix over the top of the charred broccoli. Slide the pan or dish into the oven and cook for 15-20 mins till the egg has set.
While the frittata is cooking, squeeze the juice from the lemon into a small jug. Whisk in 1 tbsp rice vinegar, ½ tbsp olive oil and a pinch of salt and pepper to make a dressing.
Toss the dressing through the peppery salad leaves in a bowl and serve with the chilli crab frittata, garnished with the remaining mint leaves.