Pat the 600g of chicken cubes completely dry with paper towels to ensure the marinade sticks properly.
Toss the chicken with lemon juice, 1 teaspoon of Kashmiri red chili powder, and salt. Set aside for 15 minutes.
In a separate bowl, whisk together the Greek yogurt, ginger-garlic paste, mustard oil, remaining Kashmiri chili, garam masala, ground cumin, and turmeric until smooth.
Combine the yogurt mixture with the chicken. Cover and refrigerate for at least 2 hours, or overnight.
Thread the chicken pieces onto wooden (soaked) or metal skewers, leaving slight gaps between the pieces so they cook evenly.
Place skewers on a wire rack over a foil-lined baking sheet. Broil on high for 12-15 minutes, flipping once, until charred spots appear on the edges.
Brush with melted butter in the final 2 minutes of cooking for a glossy, moist finish.
