Does anyone have healthy lunch suggestions? One can only subsist on sweet potatoes, apples, black beans and shredded cheese for so long.

Tomato cucumber avocado salad with simple dressing is always a good idea. I like stealing healthy suggestions from Natashaskitchen.com

Before I answer your question, I would suggest a healthy mid-day snack (e.g., an apple). The intent it is minimize the hunger you might have at lunch. It has been my experience that I eat more than I need, when I am really hungry.
Now back to your question. When my schedule permits, I get up and walk to a place for lunch. I feel the walk and fresh air, gives me a break and allows me to better focus when in return.
To your specific question about what fk