COOK pasta in a large pot of salted boiling water according to package directions; drain. Rinse pasta under cold running water until chilled. Drain well, and set aside for later use.
WHISK mayonnaise, buttermilk, garlic powder, salt and pepper together in a small bowl until combined. Set aside.
HEAT oil in a large skillet over medium-high heat. Add sausage and cook, stirring occasionally, until fully heated through, about 3 to 5 minutes.
COMBINE cooked pasta, mayo mixture, cooked sausage, bacon, romaine, tomatoes and croutons in a large mixing bowl. Serve.