1. Heat 1 tbsp oil in a medium (about 24cm) ovenproof frying pan over a medium heat. Fry the potatoes for 5 mins, tossing occasionally, until golden and starting to crisp. Transfer to a plate.
2. Add the halloumi to the pan and fry for 3 mins, turning halfway, until lightly golden but still soft; transfer to a plate. Preheat the grill to medium-high.
3. Add the remaining oil to the pan and soften the greens and chilli, if using, for 2 mins. Return the potatoes to the pan. Beat the eggs in a bowl, season, then pour over the veg. Swirl the eggs around the pan for 2 mins, then arrange the halloumi on top, pulling some of the greens so that they poke out. Dot over the tomatoes, then place under the grill for 5-6 mins until risen, golden and set.
4. Loosen the edges of the frittata, slide out onto a board and cut into wedges to serve alongside a green salad, if you like.
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