Bring a large pot of salted water to a boil. Wash and dry all produce. Trim and quarter zucchini lengthwise; cut crosswise into 1/2-inch-thick pieces. Peel and mince garlic. Zest and quarter lemon (for 4 servings, zest 1 lemon and quarter both).

Once water is boiling, add spaghetti to pot. Cook until al dente, 9-11 minutes. Reserve 1 cup pasta cooking water, then drain and set spaghetti aside. Keep empty pot handy for step 5.

Meanwhile, heat a drizzle of olive oil in a large, preferably nonstick, pan over medium-high heat. Add zucchini; cook, stirring occasionally, until browned and softened, 4-6 minutes. Season with salt and pepper. Turn off heat; transfer to a plate. Wipe out pan.

While zucchini cooks, pat chicken dry with paper towels and season all over with Italian Seasoning, salt, and pepper. Once zucchini is done, heat a large drizzle of oil in same pan over medium-high heat. Add chicken; cook until browned and cooked through, 3-5 minutes per side. Turn off heat; transfer to a cutting board to rest. Once cool enough to handle, slice chicken crosswise.

Heat a drizzle of olive oil in pot used for spaghetti over medium-high heat. Add garlic and half the lemon zest. Cook, stirring, until fragrant, 20-30 seconds. Stir in 1/2 cup reserved pasta cooking water (3/4 cup for 4 servings), stock concentrate, and juice from 2 lemon wedges (4 wedges for 4). Simmer until thickened, 1-2 minutes. Turn off heat.

Add spaghetti, zucchini, sour cream, and 1 TBSP butter(2 TBSP for 4 servings) to sauce; toss to coat. Add half the Parmesan and season with salt and pepper. (TIP: If needed, stir in more pasta cooking water a splash at a time until spaghetti is thoroughly coated in sauce.) Divide between bowls. Top with chicken. Sprinkle with remaining Parmesan and lemon zest. Serve with remaining lemon wedges on the side.