Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce.

Trim, peel, and cut carrots on a diagonal into ½-inch-thick pieces. Trim and halve zucchini lengthwise; slice crosswise into 1-inch-thick half-moons.

Trim green beans if necessary. (Save carrots for another use.)

In a medium bowl (use a large bowl for 4 servings), gently combine beef*, panko, garlic powder, salt (we used ¾ tsp; 1¼ tsp for 4), and pepper.

While everything roasts, halve, peel, and thinly slice onion. Pick parsley leaves from stems; roughly chop leaves.

Heat a drizzle of oil in a large, preferably nonstick, pan over medium-high heat. Add zucchini; cook, stirring, until softened and lightly browned, 5-7 minutes (7-10 minutes for 4 servings). Turn off heat; transfer to a plate. Wipe out pan.

Add a large drizzle of oil to same pan over medium-high heat. Add onion; cook, stirring occasionally, until browned and softened, 6-9 minutes. TIP: Lower heat and add a splash of water if onion begins to brown too quickly.

Roast meatloaves on top rack for 10 minutes (skip roasting the carrots!), then remove sheet from oven. Swap in green beans for carrots; carefully toss as instructed. Roast 12-15 minutes more.

Add cream cheese, stock concentrate, ½ cup water, and ¾ tsp sugar (1½ tsp for 4 servings) to pan with onion; cook until thickened, 1-3 minutes more.

Turn off heat; stir in 1 TBSP butter (2 TBSP for 4) and a pinch of chopped parsley. Taste and season with salt and pepper.

Carefully toss zucchini and carrots together with half the sumac (all for 4 servings).

Divide meatloaves and carrots and zucchini between plates. Spoon caramelized onion sauce over meatloaves; garnish with remaining chopped parsley. Serve.