Vegetable Tofu Soup with Lemongrass and Coconut Milk

Name: Vegetable Tofu Soup with Lemongrass and Coconut Milk
Ingredients: 5 tablespoons vegetable oil, divided; 1 large onion, chopped; 1 tablespoon finely chopped garlic; 1 tablespoon finely chopped ginger; 2 tablespoons curry powder; 3 cups vegetable stock; 1 (14 ounce) can coconut milk; 1 large yam, cut into chunks; 2 large carrots, cut into chunks; 2 ribs celery, chopped; 0.5 cup red lentils; 0.25 cup minced lemongrass; 2 tablespoons white sugar; salt to taste; 1 (12 ounce) package medium-firm tofu, cubed and patted dry