Vegetable shepherd's pie

Ingredients

• 1 ½ kg kumara, peeled and chopped
• 1 tbs olive oil
• 1 red onion, sliced
• 1 leek, sliced
• 1 stalk celery, sliced
• 2 carrots, diced
• 1 cup dried red or brown lentils, rinsed
• 1 cup water
• 1 ½ cups vegetable stock
• 425g can chopped tomatoes
• 2 tbs tomato paste
• 1 tsp soy sauce
• ½ cup frozen peas
• ½ cup frozen corn kernels
• ½ cup parsley, chopped
• salt and pepper to season
• ½ cup parmesan cheese
• 1 tsp sesame seeds