Heat oven to 450ºF.
Place lobsters in pan and chill in freezer for 15 to 20 minutes.
Meanwhile, place 1 layer of river rocks* in the bottom of a wide pot and fill with 1 inch of water. Bring to a boil over high heat until the water evaporates. Spread herbs across rocks, then quickly place lobsters on top. Cover and cook for 2 to 3 minutes. Remove and place in ice bath to halt cooking.
Lay paper towels across a cutting board. Bring one lobster to the board and, using your chef's knife, cut the lobster straight down the center, from head to tail. Remove tomalley (the green digestive gland) and discard. Remove legs and claws. Using a rolling pin, roll over legs to extract the meat. Roughly chop the meat.
Move claws to pan and roast for 4 minutes.
Meanwhile, melt the butter in a large saute pan over medium heat. Add the onions and stir to coat. Follow with the lemon zest and scallions. Once onions are translucent, about 3 minutes, add the leg meat. Remove the pan from the heat and add the crackers, tossing until all the liquid has been absorbed.
Spoon filling into the open body cavities. Brush tail meat with olive oil and place upright on the pan along with the claws. Roast until the stuffing browns and tail meat becomes opaque, 10 to 14 minutes.
Crack claws and remove the meat. Serve on top of stuffed lobster with extra-virgin olive oil on the side for dipping.
*Smooth river rocks are available from your local landscape company