Place bacon in a frypan over medium-high heat. Cook for a few minutes until just partly cooked. Set aside.
Meanwhile, bring a pot of lightly salted water to a rolling boil. Add lobster tails and boil for 5 to 6 minutes until coloured. Drain and cool slightly. Remove shells by snipping up the center with scissors and peeling away to the side.
Slice a large pocket into the side of the eye fillet (a butcher can do this for you also). Stuff the lobster tails into the pocket. Combine 1 tablespoon of butter and lemon juice; pour over the lobster tails. Close the pocket and tie the roast closed with cotton string at 3cm intervals. Place the roast in a shallow baking tray.
Bake for about 35 minutes in the preheated oven for rare, or continue to cook to your desired degree of doneness. Lay bacon over the top of the roast and continue baking until crisp.
Melt remaining 250g butter in a saucepan over medium heat. Add spring onion, wine and garlic salt. Cook until onion is tender. Slice the roast and arrange on a platter. Spoon sauce over the meat.