Preheat oven to 425°.
In a large pot bring salted water to boil.
Once water is boiling, drop lobster tails in and return to boil; simmer for 5 minutes.
Carefully remove lobster from tail in one piece and set aside.
Cut tenderloin lengthwise to within 1/2 inch of edge, leaving one side connected.
Place lobster inside tenderloin to cover entirely.
Combine butter and lemon juice and drizzle over lobster.
Wrap top of tenderloin around the lobster and tie with string.
Sprinkle with garlic salt and pepper.
Place on rack in roasting pan.
Bake uncovered for 35 to 40 minutes or until meat thermometer reads 140° to 160°.
Meanwhile cook bacon until transparent, not crisp.
Set aside to cool.
Place bacon on top of tenderloin for the last 4-5 minutes.
May be served with this optional sauce.