Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce. Zest and halve orange. Squeeze juice from half the orange (whole orange for 4) into a small bowl. Peel and mince or grate garlic. Zest and quarter lime. Slice red potatoes into 1-inch sticks. Halve, peel, and cut onion into 1-inch wedges. Trim, peel, and cut carrots on a diagonal into ½-inch-thick pieces. Trim scallions, thinly slice greens and cut whites into 1-inch batons.

To bowl with orange juice, stir in garlic, half the orange zest, half the lime zest, half the ancho chili powder, and ½ tsp Mexican Spice Blend (all the ancho chili powder and 1 tsp Mexican Spice Blend for 4 servings; save remaining Mexican Spice Blend for another use). Add a large drizzle of olive oil and juice from half the lime; season with kosher salt and black pepper. Stir to combine.

Toss red potatoes, onion, carrots, and scallion whites on a baking sheet with a large drizzle of olive oil, salt, and pepper. For 4 servings, arrange veggies across entire sheet. Pat half chicken dry with paper towels and season all over with salt and pepper. Place chicken, skin side up, between veggies (for 4, place chicken on a second baking sheet). Pour most of the marinade (save about 1-2 TBSP for next step) over chicken and rub all over (including underside) to evenly coat. Roast on top rack until chicken is almost cooked through, 30-40 minutes (you'll add rest of marinade then). (For 4, roast chicken on top rack and veggies on middle rack, swapping rack positions halfway through.) TIP: If chicken is browning too quickly, cover loosely with aluminum foil.

Once chicken and veggies have roasted 30-40 minutes, remove sheet from oven. Carefully pour remaining marinade over chicken, turning to coat. Return to top rack and roast until chicken is cooked through and veggies are tender, 5 minutes more. TIP: To ensure chicken is cooked through, insert a thermometer into the innermost part of the thigh and breast (avoiding any bones). Once chicken is cooked, the bones may still appear pink—this is OK! Remove from oven and let rest at least 5 minutes.

While chicken and veggies roast, in a second small bowl, combine sour cream, remaining lime zest, juice from remaining lime, and a pinch of remaining orange zest. Season with salt. Add water 1 tsp at a time until mixture reaches drizzling consistency.

Transfer chicken and veggie jumble to a serving plate. Drizzle with crema and garnish with scallion greens. Serve family style.