Preheat oven to 220°C Line a baking tray with baking paper. Place sweet potato, in a single layer, on tray. Spray with oil and season with salt and pepper. Roast for 20 minutes or until tender and golden.
Heat a non-stick frying pan over medium heat. Spray with oil. Add onions, garlic and spinach. Cook for 1 to 2 minutes or until spinach is wilted. Remove from heat.
Reduce oven to 180°C Spray a 20cm (base) round springform pan with oil. Spray 1 pastry sheet with oil and fold in half crossways. Place pastry sheet in pan to line base and sides. Repeat with remaining pastry (see note).
Spoon sweet potato over pastry base. Spoon over spinach mixture. Place salmon in a bowl and flake with a fork. Spoon salmon and feta over spinach mixture. Whisk eggs, milk and salt and pepper in a jug. Pour over filling.
Bake quiche for 40 minutes or until set. Cool in pan for 10 minutes. Release sides of pan. Slice quiche and serve with salad.
Note: Lining with filo pastry: Working quickly, spray 1 sheet with oil (cover remaining sheets with damp tea towel). Fold in half to form a rectangle. Place in pan. Repeat with remaining sheets, layering crossways to completely cover side of pan.