In a small bowl whisk together the oil, vinegar, mustard, and salt and pepper, to taste.
Add the pasta and the leftover root vegetables to a large serving bowl. Stir in the parsley and the sliced red onion. Toss with the vinaigrette and refrigerate to let the flavors develop, about 1 hour.
For Pot Roast:
Season the beef with salt and pepper and lightly coat with flour. Heat the canola oil in a large skillet on medium-high heat and brown the meat on all sides. Remove to a platter and set aside. Arrange the carrots, celery and onion in bottom of slow cooker and top with the seared beef. Add the broth, water, garlic, Worcestershire sauce, and thyme, and set the cooker on low for 8 hours. When finished, remove the meat to a serving platter. Let the vegetables and broth cool for about 5 minutes, then add to a blender. Slowly blend until smooth and transfer to a serving bowl. Serve the gravy with the pot roast and roasted root vegetables.
For Roasted Root Vegetables:
One hour before the pot roast is done cooking, preheat the oven to 400 degrees F. Add all the vegetables to a large bowl and add the canola oil, rosemary, thyme, and onion. Season with salt and pepper, to taste, and arrange on a sheet tray. Roast for 30 minutes, then toss and roast another 30 minutes. Arrange on a serving platter and serve.