1Place sweet potato in a single layer on a microwave-safe plate. Cover and microwave on High/100% 4-5 minutes or until almost tender. Drain and set aside to cool. Heat a non-stick frying pan over high heat. Add oil and mushrooms, cook 5-8 minutes, stirring occasionally, until golden. Set aside to cool.
2Preheat oven 180°C (fan forced). Grease and line a 4cm deep x 22cm x 28cm slab pan. Use electric beaters to beat ricotta in a bowl until smooth. Add eggs and cream cheese, beat until well combined. Season to taste.
3Drain excess moisture from mushrooms, then fold into ricotta mixture with spinach, feta, capers and sweet potato. Spoon mixture into prepared pan. Bake 45-50 minutes or until set when a skewer inserted into centre comes out clean. Set aside in pan 1 hour. Cover and refrigerate until cold.
4Cut frittata into 36 squares. Top each piece with smoked salmon and serve with lemon wedges.