In a large stockpot or Dutch oven, heat the oil. Saute the onion and carrot over medium-high heat until soft and beginning to brown, 7 minutes. Add the garlic, cumin, ginger, turmeric, chili flakes, and salt. Cook one minute more. Stir in the tomatoes, scraping up any brown bits from the bottom of the pan, and cook until the liquid has reduced and the tomatoes are soft, 5 minutes.
Add the lentils and stock. Bring to a boil, then reduce the heat and simmer uncovered until the lentils are soft, 10 minutes. Fold in the chard and cook until wilted, but still vibrant, 5 more minutes. Taste for seasoning.
Serve the soup in bowls with a wedge of lemon on the side or a dollop of Greek yogurt.