For vegetables:Place the potatoes, carrots, and onions in a large bowl. Add the olive oil and thyme, and season generously with salt and pepper, then toss until the vegetables are evenly coated. Transfer the vegetables to a baking sheet or a large cast-iron skillet, and roast for 45 minutes, or until they are tender and well browned, using a metal spatula to flip them every 15 minutes or so. Remove the vegetables from the oven, cool for 10 minutes, then add the parsley, lemon zest, and lemon juice, and toss to combine. Taste for seasonings, and add more salt or pepper, as desired.For meat: Preheat the oven to 300° F.Heat the oil in a large Dutch oven or heavy pot over high heat. Season the pot roast generously with salt and pepper, then add it to the pot, and sear on all sides until nicely brown.Transfer the roast to a plate, then pour the beer into the Dutch oven, whisk to scrape up any browned bits, and whisk down the foam. Stir in the broth, Italian dressing mix, bay leaves,garlic, and onions. Put the roast back in the Dutch oven, and bake, covered, for 3 hours, or until tender, turning once. Remove the bay leaves, and serve with roasted vegetables.