In a large, heavy saucepan, heat the oil over medium-high heat. Add the onion and saute until soft, about 4 minutes. Add the garam masala, bay leaf, and apples, and cook, stirring continuously, for 2 more minutes. Add the lentils and stock and bring the mixture to a boil over high heat. Reduce to a simmer and cook for about 25 minutes or until the lentils are tender, being careful not to overcook them. Remove the pan from the heat, remove the bay leaf, and adjust seasoning to taste. Serve the lentils hot in one large serving bowl. Serve the yogurt and apple crisps separately and invite diners to combine all three components to their personal taste. Makes 4 appetizer or 2 main course servings. APPLE CRISPS: Preheat the oven to its lowest setting. In a small bowl, dissolve the sugar in the lemon juice. Thinly slice the apples horizontally into rounds approximately 1/16-inch thick. Lay the apple slices on a baking sheet lined with parchment paper and brush lightly with the sugared lemon juice. Place the baking sheet in the oven and allow the apples to dry, about 3 to 4 hours or overnight. Remove the baking sheet from the oven and gently peel the apple slices from the paper. (Some discoloration of the apple slices will occur.) Store in an airtight container until ready to use. They will last for 2 days in the refrigerator. CURRIED YOGURT: Heat a small nonstick skillet over medium heat. Add the curry powder and toast until you can smell its intense aroma, about 30 seconds. Remove pan from heat. Combine the curry powder with the banana and yogurt in a serving bowl, stirring well. Refrigerate until ready to use. Makes 2 cups.