In a bowl combine the onion, green onion, jalapeno pepper, grapefruit segments, maple syrup, grain mustard, tarragon, and vodka. Season to taste with salt and pepper and set aside.
Place one foil sheet over the other to create a double layer. Place the snook on the foil and season with lemon pepper seasoning. Add the vegetable/vodka mixture, top with 1 tbsp. of butter and fold up the sides of the foil to create an airtight seal. Repeat with remaining fillets of fish
Preheat grill to medium high.
Place foil pouches onto the grill and close lid. Grill-bake the pouch for 15-18 minutes. Remove from grill and allow too rest for 2 minutes. Tear open each pouch allowing the steam to escape.
Serve with steamed or grilled asparagus