Intensely flavorful ginger marries well with the strong curry powder seasoning in this Indian-style lentil soup.
In a large, heavy-bottom pot, heat oil over medium-high heat. Add onion, garlic, ginger, cumin, and curry powder; cook, scraping any browned bits from bottom of pot with a wooden spoon, until onion is soft and light golden, about 10 minutes. Reduce heat to medium, and add tomatoes. Cook about 5 minutes.
Stir lentils, chicken stock, the water, and bay leaf into pot; raise heat to medium-high, and bring to a simmer. Reduce heat to low; cook, stirring occasionally, until lentils are tender, about 30 minutes. Add salt; season with pepper. Remove from heat. Let stand about 10 minutes.
Meanwhile, make fried ginger: In a medium saute pan, heat oil over medium heat. Add ginger in a single layer; cook, stirring constantly, until strips begin to turn crisp and deep golden, about 4 minutes. Using a slotted spoon or tongs, transfer to paper towels to drain. Keep warm until ready to serve.
Remove bay leaf from pot, and discard. Using an immersion or regular blender (working in batches so as not to fill jar more than halfway), puree soup until completely smooth. Return soup to low heat until warmed through. Divide soup among six serving bowls; top each bowl with about 1 tablespoon yogurt. Garnish with fried ginger; serve.
After it has finished cooking, this soup will continue to thicken; thin it with hot chicken stock or water, if desired.