Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Peel and dice sweet potatoes into 1/2-inch pieces. Trim and halve zucchini lengthwise; slice crosswise into 1/2-inch-thick half-moons. Zest and halve lemon.

Place sweet potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Drain and return sweet potatoes to pot. Mash with sour cream and 1 TBSP plain butter (2 TBSP for 4 servings). Season with salt and pepper. (TIP: If you like your sweet potatoes extra sweet, add 1/2 tsp sugar for 2 or 1 tsp for 4 while mashing.) Keep covered off heat.

Meanwhile, toss zucchini on a baking sheet with lemon zest, a drizzle of olive oil, salt, and pepper. Place lemon halves cut sides down on same sheet. Roast on top rack, flipping zucchini halfway through, until browned and tender, 12-15 minutes. Tent with foil to keep warm.

Meanwhile, pat pork dry with paper towels; prick all over with a fork or knife. Season all over with garlic powder, salt, and pepper. Heat a drizzle of olive oil in a large pan over medium-high heat. Add pork and cook until browned and cooked through, 4-6 minutes per side. (TIP: If pork begins to brown too quickly, reduce heat to medium.) Turn off heat; transfer to a plate. Wipe out pan.

Return same pan to medium-high heat. Add stock concentrate and 1/4 cup water (1/3 cup for 4 servings). Simmer until slightly reduced, 2-4 minutes. Add any resting juices from pork. Remove from heat and stir in garlic herb butter. TIP: If sauce is too thick, stir in a splash of water.

Toss zucchini with as much roasted lemon juice as you like. (TIP: Start with half, taste, and add more from there if desired.) Divide between plates with sweet potatoes and pork. Top pork with pan sauce.