In a large pot or Dutch oven, heat the oil over medium heat. Add the diced onion and sauté until translucent, about 5-7 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Add the chicken pieces to the pot, skin side down. Sear until golden brown on all sides, about 8-10 minutes.
Stir in the tomato paste, grated carrots, chopped tomato, and chopped peppers. Add whole cloves, cardamom pods, cinnamon sticks, and all ground spices (cumin, coriander, salt, allspice, paprika, and black pepper). Mix well to coat the chicken.
Rinse the basmati rice under cold water until water runs clear. Add the rinsed rice to the pot, followed by the hot water. Bring to a gentle boil.
Reduce heat to low, cover the pot, and simmer for about 30-40 minutes until chicken is cooked through and rice is fluffy and tender.
Five minutes before cooking is done, sprinkle raisins and nuts over the top. Cover and let residual heat plump raisins and toast nuts.
Remove pot from heat. Let sit for 10 minutes. Fluff rice with a fork and serve on a large platter, garnished with additional nuts if desired.