Peel the sweet potatoes, cut them in half horizontally, then slice them very thinly.
Heat the oil in a large frying pan and gently sauté the sweet potatoes for about 8 minutes, or until tender. Add the garlic and oregano and stir for a few seconds, then add the green peas and a small amount of water. Cover and steam for 3–5 minutes, until the peas are tender.
Arrange the vegetables evenly in the pan. Lightly whisk the eggs with a little salt and pepper, then pour them evenly over the vegetables.
Reduce the heat, scatter the grated Pecorino over the top, cover and cook for 8–10 minutes, or until the egg is set and the surface is no longer runny.
If you prefer a golden top, place the pan under the grill for about 1 minute, until lightly browned. You can scatter a little extra cheese over the top before grilling, if you like.
Serve warm, sprinkled with the chopped coriander. Alternatively, let the frittata cool, then cut it into small squares or thin wedges and serve as a party nibble or appetiser.