Slice the pork sausage into 1/4-inch thick, bite-sized pieces. (These sausage rolls come in different sizes. This one you see here measures 3.5 inches in diameter, so I had to quarter it.) Transfer the sausage slices to a large mixing bowl.
Add the onion, tomatoes, celery, and chilies to the mixing bowl.
Season with lime juice and fish sauce, toss, and correct seasoning as needed. I’d start out with a tablespoon each of lime juice and fish sauce since the flavors of the tomatoes and the pork sausage vary. You can always add more as needed. For this salad, I don’t add any sugar, because the tomatoes are already very sweet.
Top with cilantro leaves and serve immediately.
