Preheat the oven to 400ºF / 200ºC degrees.
Melt the butter in a large skillet over medium heat. Add in the onions, celery and carrots and cook for 5 to 6 minutes until the vegetables are tender.
Stir in the flour, thyme, salt and pepper and cook for 1 minute.
Gradually add in the broth and half and half whilst whisking.
Continue to cook until the sauce has thickened then add in the rotisserie chicken and thawed peas.
Transfer to an oven proof baking dish and top with rows of the tater tots.
Bake uncovered for around 30 minutes until the tots are golden brown and crispy.