Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Trim and halve zucchini lengthwise; cut crosswise into 1/2-inch-thick half-moons. Quarter lemon. Strip 1 tsp thyme leaves from stems; finely chop leaves.

In a small pot, combine rice, 3/4 cup water (11/2 cups for 4 servings), and a big pinch of salt. Bring to a boil, then cover and reduce to a low simmer. Cook until rice is tender, 15-18 minutes. Keep covered off heat until ready to serve.

Toss zucchini on a baking sheet with a drizzle of oil, salt, and pepper. Roast on top rack, flipping halfway through, until browned and tender, 14-16 minutes. Remove from oven and cover to keep warm.

Meanwhile, pat pork dry with paper towels; season all over with salt and pepper. Heat a drizzle of oil in a large pan over medium-high heat. Add pork and cook until browned and cooked through, 2-3 minutes per side. Turn off heat; transfer to a plate. Wipe out pan.

Melt half the garlic herb butter in same pan over medium heat. Add chopped thyme and cook until fragrant, 20-30 seconds. Stir in stock concentrate and 1/4 cup water (1/3 cup for 4 servings) and bring to a simmer. Once simmering, turn off heat. Stir in sour cream and a squeeze of lemon juice. Season with pepper.

Fluff rice with a fork; stir in remaining garlic herb butter. Taste and season with salt and pepper. Divide rice, pork, and zucchini between plates. Spoon sauce over pork. Serve with remaining lemon wedges on the side.