Slice the celery stalks into ½-inch slices on the bias. Peel the mango and dice into ½-inch cubes.
In a large bowl, toss the celery, mango, Serrano pepper, pistachios, fried lentils, mint, cilantro and black salt together. Squeeze the lemon juice over the celery mixture. Heat the olive oil in a small pan over high heat and pop the cumin seeds. Drizzle the hot oil and seeds over the celery mixture. Mix together gently. Refrigerate for 2 or 3 hours before serving. This salad should keep for about 24 hours without losing flavor.
* To make fried lentils: Soak 1 cup channa (or moong dal) in ample water (4:1 water to lentil) for 2–3 hours. Drain and spread onto a pan covered with paper towels. Dry for about an hour.
Deep-fry the lentils in oil at 300°F for 4–5 minutes, or until crisp and cooked. Take out and drain on paper towel. Transfer to a bowl and, while warm, toss with ½ teaspoon black salt and ½ teaspoon chili powder. Store in an airtight container until ready to use in salad.