Bring a large pot of salted water to a boil. Add the orzo pasta and cook according to package instructions, about 8-9 minutes, until al dente. Drain and set aside.
In a large skillet, melt the butter over medium heat. Add the finely chopped onion and cook for 3-4 minutes until translucent.
Add the minced garlic to the skillet and cook for 30 seconds until fragrant, stirring frequently to avoid burning.
Pour in the chicken broth and heavy cream, stirring to combine. Bring the mixture to a gentle simmer.
Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes.
Stir in the cooked orzo, grated Parmesan cheese, salt, black pepper, and crushed red pepper flakes. Mix well until the cheese is melted and the sauce is creamy.
Remove from heat and let the dish sit for 1-2 minutes to thicken slightly before serving.