First, gather your ingredients for the pickling spices. Ingredients include fennel seeds, fenugreek seeds, kalonji seeds, black peppercorns and mustard seeds. Further, dry roast them on medium heat on a pan until they change color and are fragrant. This step should take about 2 minutes. The spices can burn quickly so make sure you monitor them. Furthermore, let them cool.
Dice the chicken to 2-inch cubes.
In a mixing bowl make the marinade with the following ingredients. Mango pickle (just the oil and spices, not the actual mango pieces), Greek yogurt, ginger garlic paste, Kashmiri chili powder, red chili powder, lemon juice, garam masala, salt, and 2 tbsp oil (preferably mustard). Mix well.
Next grind the dry roasted achari spices into a fine powder in a coffee grinder or spice grinder. Additionally, add the ground achari spices to the marinade.
Mix well. Finally add the chopped chicken to the marinade.
Cover the marinated chicken bowl with a lid and let it sit in the chicken sit in the marinade for at least 30 minutes. If time permits you can store it in the refrigerator for 6 to 8 hours. If not, 30 minutes will suffice.