Lightly coat the inside of a 12–16-ounce microwave-safe glass or ceramic mug, or a microwave-safe glass container, with cooking spray. Use a vessel with room to stir the mixture.

Tear the tortilla into bite-sized pieces and transfer to a bowl. Add the fully cooked chicken, green enchilada sauce, and Monterey Jack and stir to combine. Transfer the mixture to the prepared mug or glass container.

Loosely cover with a microwave-safe cover or damp paper towel and microwave on high for 1 minute. Carefully uncover and gently stir the center. Re-cover and microwave for 30–60 seconds more, until the sauce bubbles at the edges and the cheese is melted. Check that the center reaches 165°F; if needed, continue heating in short intervals until it does. Do not use a sealed lid.

Let stand for 1 minute before eating. The mug or container and trapped steam will be hot, so uncover carefully and handle with care.