1. Preheat the grill to medium-high. Put the butternut and sweet potato cubes in a pan of boiling water and simmer for 5-6 minutes until tender, then drain.
2. Meanwhile, cook the onion in the olive oil over a medium heat in a small frying pan for 5-10 minutes until tender. Add the butternut and sweet potato cubes, turn the heat to medium-high and cook for 2 minutes until they turn lightly golden. Pour in the beaten eggs, feta, parsley and pine nuts and cook for 5-10 minutes until the underside of the tortilla is golden brown (use a spatula to lift the edge to check).
3. Place under the grill and cook for 5-10 minutes until the tortilla is fully set and the top is golden. Invert onto a chopping board, cut into wedges and serve with a green salad.