2 cups red lentils
3 cups water, or more as needed
1 tablespoon vegetable oil
1 large onion, diced
2 tablespoons curry paste
1 tablespoon curry powder
1 teaspoon ground turmeric
1 teaspoon ground cumin
1 teaspoon chili powder
1 teaspoon salt
1 teaspoon white sugar
1 teaspoon minced garlic
1 teaspoon minced fresh ginger
1 (14.25 ounce) can tomato puree
Wash lentils in cold water until water runs clear.
Put lentils in a pot with enough water to cover; bring to a boil and reduce heat to medium-low. Cover and simmer, adding water as needed to keep lentils covered, until tender, 15 to 20 minutes. Drain.
Heat vegetable oil in a large skillet over medium heat; cook and stir onions in hot oil until caramelized, about 20 minutes.