Cook barley according to package directions (I cooked 1 cup barley in 3 cups of water with a pinch of salt and it took about half an hour).
Meanwhile, preheat oven to 400F and move the rack to the middle position.
Prep your veggies (try to cut them into pieces that are about the same size (I aimed for about 1" pieces) so they cook more evenly) and add them to a baking sheet. Toss with the olive oil, garlic powder, Italian seasoning, and salt & pepper. Roast them for 20 minutes or until they're cooked. You can flip them halfway through if you wish, but I did not.
Add the dressing ingredients to a bowl and whisk together until smooth. Adjust the lemon juice and seasonings as needed. Thin with 1 tablespoon of water at a time until your desired consistency is reached.
Once everything is ready, you can either add it all to a large bowl or platter and assemble it like you would a salad, or you can portion it out into individual containers if you're going the meal prep route.