Heat 1–2 tablespoons olive oil in a large skillet over medium heat.

Add 1 pound chopped sausage and 1 medium chopped onion. Sauté for about 5 minutes, until the onions are translucent and the sausage starts to crisp.

Stir in 3 minced garlic cloves and cook for 1 minute, until fragrant.

Add 1 cup chopped spinach, 1 ½ cups chicken stock, ¾ cup heavy cream, 1 can Ro*Tel (with juices), ½ teaspoon salt, ½ teaspoon black pepper, ¼ teaspoon red pepper flakes (if using), and 2 cups rotini pasta. Stir well to combine.

Bring the mixture to a boil, then reduce heat to low. Cover and cook for about 20 minutes, stirring occasionally, until the pasta is tender.

Stir in ½ cup Monterey Jack cheese and ½ cup cheddar cheese until melted. Sprinkle the remaining cheese on top, cover, and let sit for 2–3 minutes to melt.

Garnish with 3 chopped green onions before serving.