England led 28-0 at the break thanks to first-half converted scores from wings Charlie Sharples and Ugo Monye, a penalty try and a hat-trick of penalties from Toby Flood.
Exeter flanker Tom Johnson crossed early in the second period to increase the lead following impressive handling from Alex Goode and captain Chris Robshaw, with Lancaster handing debuts to prop Maku Vunipola and lock Joe Launchbury either side of Johnson's first Test score.
Fiji did get on the scoreboard thanks to some lovely feet from scrum-half Nicola Matawalu but Sharples increased the lead once more after Monye was dragged down just short.
Manu Tuilagi scored a late brace to make it seven tries in all for England and a second Fiji score from Seko Kalou was nothing more than a consolation at RFU headquarters.
England will be frustrated not to have kept a clean sheet against an under strength Fijian outfit and by the number of chances they failed to take at Twickenham but Lancaster will have seen plenty of positives, including the form of man-of-the-match Goode.
The Saracens full back was a contentious choice ahead of Mike Brown but he repaid his coach's faith with a superb display in which he offered himself as a second playmaker and kept England's momentum going when it may otherwise have been halted.
Goode and his England colleagues will face much stiffer challenges over the next three weeks, though, as Australia, South Africa and New Zealand all head to London.