Preheat oven and large non-stick roasting pan to 230°C fan forced. Add the mushrooms to the hot pan, spray with olive oil and drizzle over the lemon juice. Season with salt and pepper, shake to coat the mushrooms. Roast 10-15 minutes until mushrooms are tender.
Mix egg yolks, ricotta, chives, parmesan, lemon rind and salt and pepper together with a fork. Use a hand mixer to whisk the egg whites to stiff peaks then gently fold into the egg yolks mixture.
Heat a large non-stick, oven-proof frying pan over medium-low heat. Spray the pan with oil and place four lightly greased egg rings in the pan. Spoon 2 tablespoons mixture into each ring and cook for 3 minutes. Transfer the pan to the oven and bake a further 5 minutes or until puffed and light golden on top.
To serve, place 2 omelettes on each plate. Top with a dollop of crème fraiche, spinach and serve with mushrooms.