Adjust rack to middle position and preheat oven to 450 degrees. Wash and dry all produce. Mince garlic. Trim and discard woody bottom ends from asparagus; cut stalks crosswise into 3-inch-long pieces. Strip thyme leaves from stems; roughly chop leaves. In a small pot, combine stock concentrates and 1 cup water (2 cups for 4 servings). Bring to a simmer over medium heat.

Toss garlic, asparagus, tomatoes, and half the thyme on a baking sheet with a drizzle of olive oil, salt, and pepper. Roast, tossing halfway through, until asparagus is tender and tomatoes burst, 12-15 minutes.

Meanwhile, trim and thinly slice scallions, separating whites from greens. Melt 1 TBSP butter (2 TBSP for 4 servings) in a medium pot over medium heat. Add scallion whites and cook, stirring, until fragrant, 1 minute.

Add couscous and remaining thyme to same pot. Cook, stirring, until grains are lightly toasted, 1-2 minutes.

Pour simmering stock into pot with couscous mixture. Reduce to a low simmer, then cover and cook until tender, 6-8 minutes. Drain any excess liquid from pot, if necessary.

Fluff couscous with a fork; season with salt and pepper. Divide between plates, then top with roasted veggies. Sprinkle with almonds, feta, and scallion greens.