Adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce.

Trim and dice cucumber into ¼-inch pieces. Cut cauliflower into bite-size pieces if necessary. Trim, peel, and cut carrots on a diagonal into ½-inch-thick pieces. Quarter lemon.

In a small bowl, combine cucumber, ½ tsp sugar (1 tsp for 4 servings), and salt. Set aside to marinate. (You'll finish the raita in Step 5.)

Toss cauliflower and carrots on a baking sheet with 2 TBSP olive oil, 2 tsp curry powder, salt, and pepper (4 TBSP olive oil and 4 tsp curry powder for 4 servings). (You'll use the rest of the curry powder in the next step.)

Roast on top rack until browned and tender, 15-20 minutes.

While veggies roast, pat chicken* dry with paper towels. Season all over with remaining curry powder, ½ tsp garam masala (1 tsp for 4 servings), salt, and pepper. (Save remaining garam masala for another use.)

Heat a large drizzle of oil in a large pan over medium heat. Add chicken and cook until browned and cooked through, 3-4 minutes per side.

Transfer to a cutting board.

Add yogurt, sour cream, and juice from half the lemon to bowl with marinated cucumber. Stir to combine.

Slice chicken crosswise.

Divide chicken and roasted veggies between plates. Top chicken with as much cucumber raita as you like. Serve with any remaining raita and remaining lemon wedges on the side.