Preheat oven to 350°F (175°C).
In a small bowl, mix together 1/4 cup ketchup and 1 tablespoon Worcestershire sauce; set aside.
In a large bowl, combine ground beef, Italian dressing mix, bread crumbs, eggs, fresh parsley, and the ketchup-Worcestershire mixture. Mix gently until just combined; avoid overmixing.
Transfer meat mixture onto a sheet pan lined with parchment or lightly greased, shaping it into a loaf.
Bake meatloaf for 50 minutes. Then, brush the top with the reserved ketchup mixture and continue baking for another 10 minutes, or until an internal temperature of 160°F (71°C) is reached.
Remove meatloaf from oven and let it rest for 10 minutes before slicing.
Meanwhile, place potatoes in a large pot and cover with salted water by about an inch. Bring to a boil over high heat.
Reduce heat and simmer potatoes until tender when pierced, about 15 minutes.
Drain potatoes and return them to the pot. Add heated milk, butter, and salt to taste.
Mash potatoes until smooth and creamy; then fold in sliced scallions.
Serve warm mashed potatoes alongside slices of the zesty Italian meatloaf.