Put the lentils in a large pot and cover with cold water. Swish with your hand to release surface starch, then pour off the water. Repeat this rinsing and draining until the water runs clear.
Cover the lentils with 2 quarts cold water. Bring to a simmer over medium heat, skimming any foam. Reduce the heat to maintain a gentle simmer and cook, uncovered, until the lentils are tender and beginning to fall apart, about 15 minutes.
In another large pot, warm the olive oil over medium heat. Add the onion, celery, garlic, chile, paprika, cumin, and turmeric and sauté until the vegetables are soft, about 10 minutes. Add the tomato and bay leaf and cook, stirring, until the tomato softens and the juices thicken, about 5 minutes. Stir in the cooked lentils and their liquid. Add 1 tablespoon salt. Simmer for 10 minutes, then stir in the cilantro and garam masala and taste for salt. Simmer for 5 minutes to blend the flavors. Serve immediately, garnishing each portion with a little additional chopped cilantro.
