Melt the butter in a large skillet over medium heat. Stir in the onion and ham and saute for 5 minutes, or until onion is translucent.
Pour in the half-and-half and the cheese, stirring frequently, until the sauce starts to thicken and bubble. Season with salt and pepper to taste and set aside.
Fill a large pot with water and bring to a boil. Add the tortellini and cook to desired doneness, or according to package directions. Add the peas to the boiling tortellini in the final minute of cooking. Drain all from the water and toss with the ham and sauce mixture.