Heat oil in a 9 or 10 inch skillet (preferably cast iron or ovenproof; if skillet's handle is plastic, wrap it in foil before you place it under the broiler later). Add turkey, onion and garlic; cook on medium-high heat, crumbling meat up with a wooden spoon, until it is no longer pink, about 3 minutes. Stir in kale; reduce heat to medium and stir for about 3 minutes.
Meanwhile, in a bowl, whisk eggs, egg whites and ricotta. Pour evenly over turkey mixture; cook until bottom and sides begin to firm, about 4 minutes. Sprinkle with Swiss cheese and hot pepper flakes; put under broiler until centre of frittata is set and cheese is melted and bubbly, 4 to 5 minutes.
Cut into 8 wedges and place 2 on each plate. Serve with crusty whole-grain bread if desired.
Per serving: 276 calories, 29 g protein, 14 g fat (5 g saturated fat), 8 g carbohydrates, 1 g fibre, 267 mg cholesterol, 255 mg sodium