Preheat your oven to 425°F, if you’re using the grill, set the grill up for two zone cooking and establish the temperature at 425°F as indicated by a reliable leave-in thermometer.
While the grill is preheating, cut the root ball off of the celery stalk. Then, using a sharp knife or a vegetable peeler, shave off just a thin layer on the outside of the root ball to expose a fresh root all around.
Slice the root ball into roughly 1.5 inch squares.
Put the root squares in a medium sized mixing bowl, and drizzle with two tablespoons of olive oil. Toss the root squares to evenly coat with oil. Then season with remaining ingredients, except the parsley. Toss again to evenly coat the root squares and place them in a single layer on a parchment paper lined sheet pan.
Place the pan in the oven or on the grill over indirect heat. Close the lid and allow them to roast for 22-25 minutes, till fork tender. Don’t over cook them or they will get mushy.
Remove them from the grill, drizzle with remaining olive oil and garnish with fresh parsley. Serve hot.