Bring a large pot of salted water to a boil, add penne and cook until tender with a bite, about 7 minutes; remove from heat.
Meanwhile, add kielbasa to a skillet over medium-high heat. Cook until kielbasa coins are lightly browned. Add butter; when melted, add onion and sauté until softened, about 4 minutes. Add garlic and cook until fragrant, about 30 seconds. Add in broccoli florets and mushrooms.
Pour in chicken broth, cover, reduce heat, and simmer for 5 minutes. Stir in cream, Parmesan, Italian seasoning, salt, and pepper.
Strain pasta and stir into kielbasa mixture. Serve immediately.
