Spinach, Mushroom & Feta Filo Bake

• 3 tbsp extra virgin olive oil
• 1 onion, finely chopped
• 2 garlic cloves, crushed
• 250 g mushrooms, sliced
• 250 g frozen spinach
• 200 g feta, crumbled
• 3 eggs, beaten
• 2 tsp sesame seeds
• 6 sheets of filo pastry