In a large pot, heat 1 tbsp oil over medium heat. Add onions and cook on medium-low for 6-8, stirring occasionally, until tender and slightly golden.
Add tomato, tomato paste, ginger, garlic, and spices. Cook for 3-4 min, stirring well to toast spices.
Stir in water, lentils and coconut milk. Bring to a boil over high heat. Use a spatula to scrape off any stuck-on bits on the bottom of the pot. Season with 2 tsp salt (or more to taste) and plenty of cracked pepper.
Cover and simmer on medium low for 10-12 min, stirring occasionally, until thickened. Add a 1/4 cup or more of water if it looks too thick.