Heat 1 tablespoon of the oil in a large nonstick frying pan with a heatproof handle. Add the sausages (no need to prick them) and fry over a medium heat for 10-12 minutes, turning occasionally until evenly browned. Remove, drain on kitchen paper and allow to cool slightly before cutting each one into 5 diagonal slices.
Wipe out the pan, then pour in the remaining 1 tablespoon of oil and heat up. Tip in the the sweet potato and red onion and stir fry for 10-12 minutes until softened and turning golden. Stir in the spinach for a few seconds (just enough to wilt) then return the sausages to the pan. Preheat the grill to high.
Beat the eggs, season, pour them into the pan, then scatter over with the snipped chives. Cook over a medium heat for about 5 minutes, or until the edges begin to set. Place the pan under the grill for a few more minutes until the top begins to puff up and is lightly browned. Scatter over the remaining snipped chives, and serve with a green salad.
COOK'S TIP This frittata is good served cold as well as warm – and great for taking on a picnic.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.