Heat the olive oil in a large deep skillet or Dutch oven over medium heat.
Add the sliced kielbasa and cook for 4 to 5 minutes, stirring occasionally, until browned and slightly crisp. Remove kielbasa from the skillet and set aside.
In the same skillet, add the chopped onion and cook for 3 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant, stirring constantly to prevent burning.
Pour in the chicken broth and heavy cream, stirring to combine.
Bring the mixture to a gentle boil, then add the refrigerated cheese tortellini.
Reduce heat to medium-low and simmer for 7 to 9 minutes, stirring occasionally, until the tortellini are cooked through and the sauce has thickened slightly.
Stir in the chopped baby spinach and cooked kielbasa, cooking for another 2 minutes until the spinach has wilted.
Remove the skillet from heat and stir in the grated Parmesan cheese and crushed red pepper flakes.
Season with salt and freshly ground black pepper to taste.
Serve immediately, garnished with extra Parmesan if desired.