One Pot Mushroom Stroganoff Pasta

• 1 tbsp extra virgin olive oil
• 1 brown onion, finely chopped
• 400 g mushrooms, sliced
• 400 g tin lentils
• 750 ml beef stock
• 240 ml lite coconut milk
• 300 g pasta spirals
• 1 tbsp smoked paprika
• 2 large cloves garlic, crushed
• 1 tbsp plain flour
• 0.5 lemon, juiced
• 0.25 cup parsley leaves, finely chopped
• 0.25 cup parmesan cheese to serve (optional)