Toss the quartered potatoes with the seasoning salt and olive oil.
Place in a grill basket and grill over medium-high heat for about 20 minutes, or until potatoes are soft. Toss often to prevent burning.
Once soft, mash the potatoes with a potato masher and mix in butter and milk or sour cream. Top with chopped chives or other mashed potato mix-ins.
Serve Grilled Mashed Potatoes with your favorite grilled meat and/or veggies.