Preheat oven to 400°F (200°C). (If using frozen Brussels sprouts, place in bowl of cold water 5 min. to partially thaw for easier slicing. Drain and proceed with recipe.) Trim sprouts; slice in half.
Place sprouts in 13 x 9-in. (3-L) baking dish. Mix with olive oil, salt and pepper. Spread in single layer. Roast 20 min., gently stirring occasionally to promote even cooking.
Add walnut pieces and return baking dish to oven for 3 to 4 min. to toast nuts. Transfer sprout mixture to serving bowl. Mix with dates, honey, vinegar, green onions, thyme and lemon zest to serve.