In a bowl, mix yogurt, gram flour, lemon juice, ginger-garlic paste, red chili powder, turmeric, garam masala, cumin powder, chaat masala, mustard oil, and salt to form a marinade.
Add paneer, bell peppers, onions, and tomatoes to the marinade. Mix well and let it rest for 30 minutes.
Preheat the oven to 200°C. If using wooden skewers, soak them in water for 10 minutes to prevent burning.
Thread the marinated paneer and vegetables onto skewers, alternating between ingredients.
Place the skewers on a lined baking sheet or grill pan and cook for 12-15 minutes, turning occasionally. Baste with butter for a smoky flavor.
Once golden and slightly charred, remove from the oven.
Serve hot with mint chutney and lemon wedges.