Preheat the grill to medium-high.
Cut the lobster tails in half down the center lengthwise. Remove the vein that runs down the center.
Stir together the butter, beer, garlic powder, and salt. Brush the inside of the lobster tails liberally with butter.
Place lobsters on the grill cut side down, close the lid of the grill, grill for 4 minutes.
Turn the lobsters over, brush again with the butter mixture. Close the lid of the grill and cook for 5 more minutes or until cooked through.
Stir together all the chimichurri ingredients.
Serve the lobster tails along side the chimichurri.