Add some basmati rice, and you've got one crazy-hearty curry.
Rinse the lentils in cold water until the water clears up. Put them in a pot with enough water to cover them. Get the pot boiling, then put a cover on, turn the heat down to medium-low, and simmer. Make sure to add more water in to keep the lentils covered until they're tender, 15 to 20 minutes. Drain the pot.
Heat the veggie oil in a big skillet over medium heat. Cook and stir the onions in hot oil until they're caramelized, around 20 minutes.
Mix the curry paste, curry powder, turmeric, cumin, chili powder, salt, sugar, garlic, and ginger together in a big bowl, then stir that mix into the onions. Turn the heat up to high and cook, stirring constantly, until the onions are fragrant, 1 to 2 minutes.
Stir the tomato puree into the skillet, then take the skillet off the heat and stir that mix into the lentils.