• Season the chicken with salt and pepper.

In a pot over medium-high heat, warm 2 tablespoon oil until hot but not smoking. Add the chicken and cook, turning once, until lightly browned, 3 to 4 minutes on each side. Transfer chicken to a plate to rest.
While the chicken browns, prepare the vegetables.

• Peel the onion and coarsely chop.
• Scrub and cut the carrot diagonally into ¼-inch-thick pieces.
• Peel the ginger and finely chop.
• Finely chop the garlic.
• Coarsely chop the cilantro, including the stems.

Add the onions to the pot used to brown the chicken, reduce the heat to medium, and cook until softened, 3 to 4 minutes. Add the carrots, garlic, ginger, and the Indian spice blend, and cook until fragrant, 1 to 2 minutes.
Return the chicken to the pot, add the diced tomatoes, 1 cup water, and half the cilantro. Bring to a boil, reduce to a simmer, cover, and cook until the carrots are tender, the chicken is cooked through, and the liquid has reduced by about half, 15 to 18 minutes.
Remove from the heat, stir in the remaining cilantro, and season with salt and pepper. While the chicken and vegetables cook, prepare the naan.

In a dry pan over medium heat (or directly over a low flame on the stove top), warm the naan until lightly toasted, 30 seconds to 1 minute on each side. Cut the naan in half.

Transfer the chicken and vegetables to individual plates. Garnish with the yogurt, sprinkle with sumac, and serve with the naan on the side.