In a large saucepan, cook the sausage in hot oil over medium heat until browned, about 6 minutes. Transfer 1/4 cup to a container and reserve for Friday. Add the onion to the pan and continue cooking until soft, 3 more minutes.
Add the tomatoes, beans and 1 cup water to the pot. Season with pepper. Simmer until the beans are warmed through and flavors have melded, about 15 minutes. Add the arugula and cook until just wilted.
