In a large skillet, heat oil over medium-high. Add chicken and cook 2-3 minutes per side until lightly browned.
Move the chicken aside and add onions, salt, pepper and garlic powder. Sauté for 3-5 minutes until tender and starting to caramelize.
Position the chicken in the center of the skillet. Spread onions around the edges and place the potatoes on top. Pour the vinegar and water evenly over the dish. Sprinkle the thyme over top.
Cover and let cook on medium for 10 minutes. Stir and add an additional ¼-1/2 cup of water if needed.
Let cook 5-10 additional minutes until the potatoes are softened. Add the frozen vegetables to the dish and cook until warmed, about 3-5 additional minutes. Stir and serve.
Notes
LeftoversStore leftovers in an airtight container in the refrigerator for up to 4 days. I don't recommend freezing as it may change the texture of the potatoes.