Prepare all ingredients as described above.

Make potato salad: Boil diced potatoes in salted water until fork-tender. Drain and spread in a single layer to cool. Mix cooled potatoes with red onion, celery, carrot, scallions, and mayonnaise. Season with salt and pepper. Refrigerate until ready to serve.

Heat the olive oil in a skillet over medium heat. Sauté the green and red bell peppers and onion until tender and golden brown, about 7–10 minutes. Remove from heat and season with salt and black pepper to taste.

Preheat a grill or grill pan on medium heat. Grill the sausage links until nicely charred on all sides and reach an internal temperature of 160°F (71°C) for safe consumption.

Place each grilled sausage link into a prepared bun. Top with the sautéed peppers and onions, and add ketchup and yellow mustard as desired.

Prepare Mango Lassi: In a blender, combine mango, yogurt, milk, cardamom, and sugar. Blend until smooth. Adjust sweetness to taste.

Serve the grilled sausage in a bun topped with grilled onion and pepper alongside the potato salad and mango lassi.