Preheat your oven to 425°F. Line a large baking sheet with parchment paper.
Add the green beans and carrots to a large bowl. Toss with the olive oil, minced garlic, salt, pepper, onion powder, and dried thyme. Stir in the lemon juice if using.
Spread the seasoned vegetables in a single layer on the baking sheet. Roast until tender and browned, about 22-27 minutes. Stir halfway for even cooking.