Combine ginger, garlic, fresh chili, yogurt, salt, spices, and sugar in a freezer bag, bowl, or container. Add chicken pieces and toss to coat evenly. Let marinate for 15 minutes or up to a day in the fridge.
Preheat the oven to 425°F. Coat a half-sheet pan with 1 tablespoon of olive oil. Add potatoes, cauliflower, salt, cumin or coriander seeds, and drizzle the remaining 2 tablespoons of olive oil over the vegetables.
Remove chicken from marinade and leave excess behind. Make spaces in the vegetables for chicken parts throughout the pan. Roast in the oven for 25 minutes, then toss the potato and cauliflower to ensure they’re cooking evenly, and return the pan to the oven for about 5 more minutes. To get a little more color on the veggies and chicken, switch the oven to broil, move the pan to the top rack, and broil for about 4 minutes.
While everything is roasting, make the lightly pickled onion rings. Separate the rings and toss them in a small bowl with a squeeze of lemon juice and a pinch of salt. Set aside until ready to use.
Top individual servings with pickled onions, dollops of yogurt, and fresh herbs.