Preheat the oven to 400 degrees F.

Set up a large steamer. Place the lobster tails in the steamer and steam until just cooked through, about 6 minutes. Remove the lobster tails from the steamer. Cut along the underside of the shell and remove the tail meat whole. Set aside

In a large skillet, heat 1 teaspoon of the oil over medium-high heat. Add the pancetta and cook, stirring, until crisp and the fat is rendered, about 5 minutes. Remove with a slotted spoon. Drain off all but 2 teaspoons of fat from the pan. Add the shallots and celery and cook, stirring, until soft, about 2 minutes. Add the garlic and cook, stirring, for 30 seconds. Add the mushrooms and a pinch each of salt and pepper, and cook until the mushrooms give off their liquid, 3 to 4 minutes. Add the green onions and stir. Add the wine, increase the heat, and cook until it has nearly all evaporated, 1 to 2 minutes. Add the parsley and stir. Remove from the heat, stir in the cooked pancetta, and let cool.

Spread the butterflied beef, cut side up, flat on a surface. Spread the pancetta-vegetable mixture in a line across the meat, about 2 inches from the top, leaving a 1/2-inch border on the sides. Lay the lobster tails on top of the mixture, going across the beef. Pull the top flap over the lobster tails and roll the meat over the stuffing, jellyroll fashion, and tuck in the ends. Tie with kitchen twine every 2 inches.

Place in a large heavy roasting pan, rub on all sides with the remaining 2 teaspoons olive oil, and season lightly with salt and pepper. Place over medium-high heat and sear the meat on all sides, about 6 minutes. Place in the oven and roast to desired temperature, 30 to 35 minutes for medium-rare.

Transfer to a cutting board. Tent and let rest for 10 minutes before carving. Remove the kitchen twine and slice thickly. Place on a platter, surround with the asparagus, and drizzle with the Bearnaise Sauce. Serve immediately.