Cut the cauliflower into small 1" pieces, discarding the thick stems. Toss on a baking sheet with olive oil, thyme, ¼ teaspoon of the salt, and black pepper and set aside.
In a large bowl, mix together the ground beef, egg, breadcrumbs, garlic, cumin, coriander, remaining ½ teaspoon salt, and pepper until well combined. Form into 1 ½ to 2" meatballs and nestle between the cauliflower on the baking sheet.
Bake until the meatballs are browned and cooked all the way through (no longer pink in the middle) and the cauliflower is tender when pierced with a fork, about 14 to 16 minutes.
Serve warm with whole-wheat couscous and tzatziki sauce.