Heat oven to 450ºF.
Place the lobsters in a roasting pan and chill in the freezer for 15 to 20 minutes.
Meanwhile, place 1 layer of river rocksSmooth river rocks are available from your local landscape company. in the bottom of a wide 12-quart pot and fill with 1 inch of water. Bring to a boil over high heat. Spread the herbs across the rocks, then quickly place the 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. Snip off the joint of each leg with kitchen shears. Using a rolling pin, roll over the legs to extract the meat. Roughly chop the meat. Repeat with second lobster
Move the claws to a half sheet pan and roast for 4 minutes.
Meanwhile, melt the butter in a 10-inch sauté pan over medium heat. Add the onion and stir to coat. Once onion is translucent, about 3 minutes, add the lemon zest and leg meat and stir to combine. Remove the pan from the heat, add the crackers, and toss until all the liquid has been absorbed.
Make a dish out of aluminum foil, shaping it so that the lobster bodies can lay flat in it. Spoon the filling into the open body cavities. Brush tail meat with olive oil and place the foil dish with the bodies on the pan along with the claws. Roast until the filling browns and the tail meat becomes opaque, 12 to 16 minutes.
Crack the claws and remove the meat. Serve on top of stuffed lobster with extra-virgin olive oil on the side for dipping.