Adjust racks to top and middle positions, then preheat oven to 450 degrees. Wash and dry all produce. Trim and dice zucchini into 1/2-inch pieces. Dice potatoes into 1/2-inch pieces (no need to peel). Pick 1 TBSP thyme leaves (2 TBSP for 4 servings) from stems; finely chop. Discard stems.

Toss zucchini on a baking sheet with a drizzle of oil and a large pinch of salt and pepper. Toss potatoes on a separate baking sheet with a large drizzle of oil, salt, pepper, and half the chopped thyme. Roast zucchini on top rack and potatoes on middle rack, tossing halfway through, until golden brown and tender, 25-30 minutes. TIP: Check periodically; zucchini may be done before potatoes

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

Heat a drizzle of oil in pan used for pork over low heat. Add remaining chopped thyme. Cook until fragrant, about 30 seconds. Whisk in jam, mustard, stock concentrate, and 1/4 cup water (1/3 cup for 4 servings). Simmer until thickened, 1-2 minutes. Stir in 1 TBSP butter until melted. Taste and season with salt and pepper.

Add pork to pan and turn a few times to coat in sauce. Turn off heat.

Toss roasted zucchini and potatoes together. Divide between plates. Top with pork and any remaining sauce.