Preheat oven to 425°F. Line a 9x13 pan with aluminium foil and set aside.
In a medium sized bowl, toss carrots and onions with olive oil, garlic powder, and salt+pepper to taste. Layer onto the prepared sheet pan and set aside.
In the same bowl, toss chicken, garlic powder, rosemary, and salt+pepper to taste. Arrange the thighs on top of the vegetables. Don't spread them flat or they will dry out. Leave them in the compact shape they come out of the package in to bake.
Bake for 35-40 minutes until carrots are tender and chicken is fully cooked. Let rest for 5 minutes before serving.