Fill a medium saucepan to a depth of 2 inches to a boil over high heat. Arrange green beans in a steamer basket and set the basket in the saucepan. Cover and steam the beans until tender, about 8 minutes.
In a small bowl, stir together parsley, capers, lemon juice and oil. Season with salt and pepper.
Arrange arugula, avocado, tuna and beans on serving plates; spoon dressing over top.
Before her diagnosis, Caroline wrote a book on cakes called Cake Magic!. She started developing a birthday cake using her gluten-free mix found in that book. Check out other recipes she’s developing for her new life—and the stories behind them—on her blog, The Wright Recipes. Her next book, Catalan Food, written with chef Daniel Olivella, comes out in early September from Clarkson Potter.