In a medium saucepan over medium heat, combine lentils with 3 cups of water. Simmer until tender, about 10 minutes. Drain and set aside.
In a small mixing bowl, combine the curry paste, curry powder, turmeric, cumin, chili powder, salt, sugar, garlic, and ginger; set aside.
Into a medium-size skillet over medium-high, heat the oil and cook onions 3 minutes, until tender and slightly caramelized.
Stir in the curry mixture, tomatoes, and cooked lentils. Reduce to low heat and cook for 5 minutes, stirring occasionally, until heated through.
Top with cilantro and serve hot.