Combine the meatloaf mix, panko, eggs, 3/4 cup ketchup, 1 tablespoon Worcestershire sauce, the scallions, parsley, thyme, 1 teaspoon salt and a few grinds of pepper in a large bowl; mix with your hands until just combined. Form into a 5-by-9-inch loaf.
Transfer the meatloaf to a 6-quart slow cooker. Scatter the potatoes and carrots over and around the meatloaf. Pour in the chicken broth. Cover the slow cooker and cook 8 hours on low or 4 hours on high.
When the meatloaf is done, skim off any excess fat from the juices in the slow cooker. Combine the remaining 1/2 cup ketchup, 1 tablespoon Worcestershire sauce and the brown sugar in a small bowl, then whisk in 1/4 cup juices from the slow cooker. Brush the top of the meatloaf with the ketchup mixture. Cover the slow cooker and let the meatloaf rest, 10 minutes.
Remove the meatloaf from the slow cooker and slice in half. Serve half with the vegetables; top with more parsley. Reserve the remaining half for Meatloaf Quesadillas.