Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Dice potatoes into ½-inch pieces. Toss on a baking sheet with a drizzle of olive oil, salt, and pepper. Roast on top rack, tossing halfway through, until browned and tender, 20-25 minutes.

Meanwhile, halve, peel, and mince shallot. Strip 1 tsp rosemary leaves from stems (2 tsp for 4 servings); discard stems and finely chop leaves. Halve lemon.

Pat chicken dry with paper towels and season all over with salt and pepper. Heat a drizzle of olive oil in a large pan over medium-high heat. Add chicken and cook until browned and cooked through, 5-7 minutes per side. Remove from pan and set aside to rest. Lower heat under pan to medium.

Add shallot, chopped rosemary, and a drizzle of olive oil to same pan. Cook, stirring, until softened, 2-3 minutes. Stir in vinegar and jam. Simmer until syrupy, 1 minute. Stir in stock concentrate and ¼ cup water (⅓ cup for 4 servings). Let reduce until thick and glossy, 2-3 minutes. (TIP: Add a splash of water if mixture is too thick.) Turn off heat. Stir in 1 TBSP butter (2 TBSP for 4). Season with salt and pepper.

While sauce simmers, in a medium bowl, toss mixed greens with a squeeze of lemon juice and a drizzle of olive oil. Season with salt and pepper.

Thinly slice chicken; divide between plates with roasted potatoes. Drizzle chicken with sauce. Serve with salad on the side.