Heat 1 tablespoon oil in a large saucepan over medium. Add garlic, ginger, cumin, turmeric, coriander, and cayenne; season with salt and pepper. Cook, stirring, until fragrant, about 30 seconds. Add lentils and broth; bring to a boil. Reduce to a simmer; cover and cook until lentils are soft, 7 to 9 minutes. Working in batches, transfer to a blender and puree soup. Return soup to pot, add 2 cups of water. Cook over medium until warmed through. Remove from heat and stir in lemon juice.
Meanwhile, heat remaining 2 tablespoons oil in a large nonstick skillet over medium-high. Add chickpeas; cook, stirring occasionally, until golden brown and crisp, 7 to 8 minutes. Serve soup topped with chickpeas and scallion greens with rice alongside.