Keto Cheesy Cabbage Sausage Skillet

unsalted butter1 (13oz) package Kiolbassa Roasted Garlic Smoked Sausage 1 red bell pepper, diced1/2 white onion, diced3 cloves garlic, minced1/2 small head cabbage, cored and chopped1 cup diced tomatoes2 cups shredded mozzarellaSalt and pepper, to taste