Add the cream and broth to a mug and heat for 1 minute. Remove from microwave. Whisk cornstarch into cream mixture 1 teaspoon at a time to prevent clumping. Stir in salt, pepper, and onion powder. Add chicken and vegetables to mug in batches, stirring after each addition to coat.
Unroll crescent dough, cut into a piece that covers the top of the mug. Poke dough with a knife to vent. Cook in microwave for 6 minutes.