Freshly grind the fennel seeds, fenugreek seeds, kalonji, black peppercorns, and cardamom seeds.
Add the freshly ground spices and all remaining ingredients to a large bowl and mix well. Add the chicken pieces and mix until well combined.
Allow the mixture to marinate in the fridge for 2-8 hours. Take it out 30 minutes before grilling to allow the chicken to come to room temperature.
Thread the pieces of the chicken onto skewers.
Grill on high heat (lowering to medium-high if needed) until golden brown and cooked through, turning skewers occasionally.
Transfer skewers to a platter and serve on top of grilled onions, bell peppers and lemon wedges.