Heat a tablespoon of oil in a large deep pan over medium heat until shimmering and fragrant.
Add the chopped onion and cook, stirring occasionally, until translucent and soft, about 7 minutes. The onions should be glossy and slightly golden at the edges.
Stir in the minced garlic and grated ginger, cooking until fragrant, about 1 minute. You’ll notice a warm aroma filling the kitchen.
Add toasted cumin seeds, coriander powder, and turmeric. Stir well and cook for another minute until the spices release their aroma and turn a richer color.
Pour in the rinsed red lentils and stir to coat them evenly with the spice mixture, allowing them to absorb the flavors for about 1-2 minutes.
Gradually add 4 cups of water or broth, stirring gently, then bring the mixture to a boil. You should hear a lively bubbling sound.
Lower the heat to a gentle simmer, uncovered, and cook for 20-25 minutes, stirring occasionally, until the lentils are meltingly soft and the sauce has thickened to a creamy consistency. The lentils will break apart slightly, creating a velvety texture.
Check the seasoning, then squeeze in fresh lemon juice to brighten the flavors. Adjust salt to taste.
Remove the curry from heat and let it sit for 5 minutes to allow the flavors to deepen and meld together.
Serve the hearty, velvety lentil curry hot, garnished with fresh herbs if desired, alongside rice or naan for a complete meal.