How do efficient employees get around being rewarded with more work?

It's important for employees to be proactive and choose the work that they want to expand. So not avoiding work, but making things efficient so they're maintained more easily! And maybe the manager doesn't know how to delegate or estimate the demand for employees' time? Do they need a full-time employee? Just telling your employees to delegate work isn't sufficient, if managers aren't willing to help initiate projects.

By not offering, or not accepting the extra work when asked, in my opinion. I make it clear that I am quite busy enough, thanks just the same.

Be honest with boss/manager.

Request training and/or certifications. Do your own research and show your manager the exact training and/or certifications you'd like then have an open conversation about it. It should be at least somewhat related to your role, of course. Training and certifications can make you not only a more valuable employee to the company but can boost your career, potentially making you more attractive to future employers as well.

There are no incentives to do a better job most people slow down and try to “keep their heads down” so they don’t get saddled with larger work loads

Nice try, we’re not falling for it.

They get around by changing jobs

Open talks with their managers.

Most organization strive to be effective; yet, some hire inefficient employees. When they identify individuals who meet their expectations those individuals are burdened down with additional work, to satisfy organizational expectations.

Speaking up when the task should go to someone else.

There is an inherent reward in getting more work... otherwise there wouldn't be the drive to be efficient. In addition, employees that are more efficient often free up their time to think further in advance or think about big picture initiatives. They are able to carve out a unique position of value for themselves in their company, by announcing and even leading independent initiatives.

You have to dumb down your work style so that you are viewed as a mediocre employee, like the inefficient ones, as efficiency is definitely frowned upon here, and mediocre is rewarded.

The boss wants to make sure it's done right.