Tuna Lasagne

• 1 tbsp extra virgin olive oil
• 1 brown onion, finely chopped
• 2 zucchini, roughly chopped
• 4 garlic cloves, crushed
• 400 g can diced tomatoes
• 500 ml passata
• 200 g smooth ricotta
• 1 tsp oregano
• 600 g can tuna in oil, drained, flaked into large pieces
• 8 instant lasagne sheets
• 1.5 cup grated cheese
• 0.3 cup fresh continental parsley leaves