Pre-heat oven to 195C-400F.
Heat the olive oil in an oven-safe 9-inch sauté pan or cast iron skillet, over medium heat. Add the chopped sweet potatoes and onion and sauté for 2 mins.
Cover the pan and reduce heat to avoid browning too much the content. Continue to cook until the sweet potato is tender and cooked through, about 5 mins.
In the meantime, mix the eggs in a blender until light and airy. Then transfer in a large bowl and mix in spinach leaves, spring onion, aromatic herbs and parmesan if using. Season with salt and pepper.
Once the sweet potato is cooked through, remove half the amount from the pan and gently mix into the egg mixture.
Pour the egg & veggies mixture into the skillet and evenly distribute over the pan.
Bake in the oven for 15-20 mins, until crispy and golden on top.
Serve it hot straight from the pan, and use any leftovers to make sandwiches the next day.