I'd say extend the top "flat surface" forward a bit, then add a simple "bridge dome" on top, near the front of it.
Then again, it may seem weird if the "structure" behind that surface is supposed to be impulse engines?
EDIT:
Some suggestions

Added "Prometheus"-esque impulse engines to the saucer, extended the flat surface forward, and gave the back-end a few windows (Observation Lounge possibly?!?)