Wash the lentils in cold water until the water runs clear. Put lentils in a pot with enough water to cover. Bring to a boil, place a cover on the pot, reduce heat to medium-low, and simmer until tender, adding water during cooking as needed to keep covered, approximately 15 to 20 minutes. Drain and set aside.
Heat olive oil in a large skillet over medium heat. Add onion, stirring frequently, and cook until caramelized, approximately 20 minutes.
In a small bowl, combine curry paste, curry powder, turmeric, cumin, chili powder, salt, garlic, and ginger.
Stir curry mixture into onions. Increase heat to high and cook, stirring constantly, until spices are fragrant, approximately 1 to 2 minutes.
Add tomato sauce to onion mixture, stirring to combine.
Remove from heat and add cooked lentils, stirring to completely combine.
Let cool slightly and serve with your favorite side dish.