Place sweet potato in a steamer basket over a saucepan of boiling water. Cover and steam for 15 minutes or until just tender. Whisk together the eggs, feta, herbs and milk in a large bowl. Add sweet potato and stir. Season with salt and pepper.
Heat macadamia oil in a frying pan; add onion and pancetta and cook, stirring occasionally, for 5 minutes or until light golden. Reduce the heat to low, add the sweet potato and egg mixture to the pan, shake evenly to distribute the egg mixture and cook for 5-8 minutes or until the frittata is set around the edge but still runny in the centre.
Sprinkle macadamias over the frittata and place pan under the grill until the frittata is golden brown and just set.
Serving suggestion: Serve with green salad topped with balsamic and macadamia oil dressing.