What is the easiest way to lose weight once you've hit a plateau?
Manipulate your diet again.
If you've been in a sustained caloric deficit, then your body probably adapted to the lower level of calories. The best thing you can probably do at this point is to start re-introducing calories back in so your highest calorie tolerance without any notable weight gain. So if you've been eating 1800 calories and your weight loss has plateaued, you can probably eat as many as 2000 calories per day and not see any sustained weight gain.
Eat at this level for several weeks and allow your body to become accustomed with its new set point weight. You'll probably note at some point that this calorie consumption will start causing some weight gain. This is a good thing, and will tell you that you can re-introduce a calorie deficit again and begin to see results again.
Another option is to just allow yourself a cheat day or 2, and load up on as many calories as you can, and then return to your dieting protocol. This will give your body and mind a reset before jumping back into a more structured diet.