Remove and discard casing from sausage; cut into 1/2-inch slices.
Cook sausage in hot oil in a large skillet over medium-high heat, stirring occasionally, 8 to 10 minutes or until lightly browned. Drain well on paper towels, and return to skillet. Add chili powder, stirring to coat sausage. Stir in chicken broth and tomato paste, stirring to loosen particles from bottom of skillet.
Stir in shell macaroni; return to boil. Reduce heat to medium-low; cover, and simmer, stirring occasionally, 8 to 10 minutes or until shells are tender.
Stir in cheese sauce from packet and tomatillo salsa; simmer, uncovered, 5 minutes or until thoroughly heated. Serve immediately with desired toppings.