Heat 2 tablespoons oil in a medium saucepan over medium heat. Add 1 cup chopped onion and cook, stirring occasionally, until softened, about 3 minutes. Add 1 tablespoon garlic, 2 teaspoons turmeric, 1 teaspoon ginger and ½ teaspoon cumin; cook, stirring constantly, until fragrant, about 1 minute. Stir in 4 cups broth, 1 cup lentils, 1 can chickpeas and ¾ teaspoon salt. Bring to a boil over medium-high heat. Reduce heat to medium-low to maintain a simmer; cover and cook, stirring occasionally, until the lentils are tender, 30 to 40 minutes.
Remove from heat and stir in 1 cup chopped spinach, 1 cup green beans and 1 tablespoon lemon juice, stirring until the spinach wilts and the green beans are heated through, about 1 minute. Ladle the soup into 6 bowls; sprinkle with 1 teaspoon crushed red pepper and garnish with a sprig of cilantro, if desired.
