Heat one tablespoon of olive oil in a large, heavy-bottomed skillet over medium heat.
Cook the sausage on the skillet until lightly browned, about 3-4 minutes. Make sure to stir well and break the sausage up while doing so.
Add the water, 4 Tbsp olive oil, garlic, chopped tomatoes, red pepper flakes and sage, stirring occasionally until slightly thickened, about 5 minutes.
Add the beans.
Season to taste with pepper.
Simmer a few minutes longer, stirring gently, until sausage is cooked through and the sauce has thickened. Be careful not to break up the beans.
Sprinkle with red pepper flakes if desired.