Cook the lentils in a medium saucepan of boiling water for 25 mins or until tender. Drain well.
Preheat oven to 200°C. Line a baking tray with baking paper. Heat a large non-stick frying pan over medium heat. Add the onion, garlic and 2 tablespoons water and cook, stirring, for 3 minutes or until tender. Add the lentils and silverbeet and cook, stirring, for 3 minutes or until silverbeet wilts. Transfer mixture to a large heatproof bowl. Cool slightly. Add the ricotta and oregano to the silverbeet mixture and fold to combine.
Place 1 sheet of pastry on the lined tray and spray with a little olive oil spray. Top with another filo sheet at a 45-degree angle and spray with olive oil spray. Continue layering with remaining filo and olive oil spray, turning each filo sheet at a 45-degree angle. Spoon ricotta mixture into the centre of the pastry and carefully scrunch up the edges of the pastry around filling to partially enclose. Sprinkle with pine nuts. Bake for 20-25 minutes or until pastry is golden and crisp.
Meanwhile, to make the salad, combine the lettuce, tomato, cucumber and onion in a large bowl. Combine the vinegar, oil and mixed herbs in a screw-top jar. Shake to combine.
Drizzle the salad with the dressing. Season with pepper. Serve with the pie.