Clean the grill grates then grease using vegetable oil, a folded paper towel and tongs. Dip the paper towel in the vegetable oil and rub on the grates holding the folded towel with the tongs. Be sure to cover the area where the lobster will be grilled.
Preheat gas grills to medium high, about 400°F to 450°F.
In a small saucepan melt 1 tablespoon butter over medium heat. Add the garlic and cook, stirring frequently, for about 2-3 minutes or until fragrant and starting to brown. Remove from the heat, transfer to a small bowl and cool slightly. Add the remaining 3 tablespoons of butter, lemon juice, lemon zest, parsley and salt. Stir to combine and set aside.
Using kitchen shears, make a lengthwise cut through the shell down the back of each lobster tail, stopping when you reach the tail fin. Turn the tails around and using the shears, cut the top tail fin to meet the other cuts. Using a sharp knife, cut through only the lobster meat following the line you just made in the shells. Don't cut through the bottom shell portion, just the lobster meat.
Turn the tails over and snip the horizontal spines down the middle of each lobster with the shears. If there are little legs on the bottom, pull them off and discard. Gently pull each lobster tail apart, to open like a book. If there is still an intestinal track (like a vein down the back of a shrimp), remove and discard. Brush the exposed lobster meat with some of the lemon garlic butter.
Place the lobster, meat side down on the prepared grate, close the lid, and grill for 5 minutes or until lightly marked. Turn the tails over and baste generously with the remaining butter mixture. Close the lid and grill until the lobster meat is firm, moist, and opaque, 2 to 3 minutes more. If using an instant-read thermometer, the meat will be done when it reaches 145°F.
Serve warm or room temperature with additional melted butter for dipping.