Heat olive oil in a large saucepan over medium-low heat. Add curry powder; cook until fragrant, about 1 minute. Add onion, ginger, and garlic; cook until onion starts to soften and is well coated with curry mixture, 2 to 3 minutes. Add cilantro, tomatoes, apples, and chickpeas. Cover; simmer until apples are tender, 30 to 40 minutes. Uncover; simmer until slightly thickened, about 5 minutes. Remove from heat, and stir in lemon juice. Just before serving, stir in yogurt.