In a large saucepan, heat butter (or dairy-free butter) over medium-high heat; saute minced garlic until tender.
Sprinkle gluten-free flour, onion powder, thyme over the sauteed garlic.
Add the chopped cooked chicken to the soup and stir to combine. Reduce the heat to low/simmer and stir in the milk (or dairy-free milk). Simmer, uncovered for about 10-15 minutes. Make sure you stir it occasionally and remove the soup from the heat as soon as it becomes as thick as you want it.