1. Heat 1 tablespoon olive oil in a medium-sized, deep frying pan and cook onion, peeled and finely sliced, for 10 minutes until soft.
2. Meanwhile, peel, halve and thickly slice baking potato, and boil for 10 minutes until tender. Drain and add to the onions in the pan.
3. Preheat the grill to medium. Lightly beat eggs until combined. Stir in ham, roughly chopped; tomatoes, chopped; Cheddar, grated; and fresh basil, roughly chopped. Season with salt and pepper and pour the mixture into the frying pan. Fry for 5-10 minutes on a low heat, gently moving the mixture around until it starts to set.
4. Once the frittata is set, but still a little wobbly on top, place under the grill until fully set. Allow the frittata to rest for a few minutes, then turn out onto a plate. Cut into wedges. Serve with salad if you wish.