If you would like softer roasted green beans, you may steam them about 5 minutes before roasting.
Combine balsamic vinegar, honey, thyme and garlic in a small bowl and set aside.
Adjust your oven rack to the middle postiion; heat oven to 450*F. Line a baking sheet with foil; spread beans on the baking sheet along with the onion wedges. Drizzle with oil. Using your hands, toss to coat evenly. Sprinkle with 1/2 teaspoons salt, toss to coat, and distribute in an even layer. Roast 10 minutes. Remove baking sheet from oven. Using tongs, coat beans and onion evenly with vinegar/honey mixture; redistribute in an even layer. Continue roasting until onions and beans are dark golden brown in spots and beans have started to shrivel, 10 to 12 minutes longer. Adjust seasoning with salt and pepper and toss well to combine. Transfer to a serving dish, sprinkle with 1/3 cup toasted and chopped walnuts. Serve and enjoy!