Here's the good thing about NASA's hardware: it usually has a docking port. Orion might be small, but so was the Apollo Command Module. However, once in orbit, you can rendezvous with something else that is already up there (or launched on the same rocket stack if you want to go 1960s mega-rocket) that has the supplies necessary for the journey, landing and stay. Then, when they blast off the surface of Mars, they rendezvous with another remote-controlled spacecraft following behind that is in Mars orbit, which has all the supplies necessary for the trip back, as well as a fresh booster filled with fuel for the return trip.
The astronauts could even do the remote control of the second spacecraft for Mars orbital entry and docking from the first in order to get around the transmission lag time inherent in any Mars mission. After all, most astronauts are accomplished pilots, and they're all pretty smart.