Add olive oil to a large, deep skillet over medium high heat. Once hot, add the sliced kielbasa and diced onions. Cook for 6-8 minutes or until browned and onions are tender. Add the garlic and cook until fragrant, about 30 seconds.
Add chicken broth, tomatoes, pasta, milk, and black pepper. Simmer for 15 minutes, or untill pasta is tender.
Remove skillet from heat and stir in ¼ cup cheese. Top with remaining cheese and cover until cheese is melted. Sprinkle with sliced scallions and serve.