Preheat your oven to 375°F and get the frozen peas and carrots out of the freezer. You can leave these out at room temperature to thaw slightly while you're getting started on the chicken and rice.
Combine the kosher salt (2 teaspoons), pepper, garlic powder, onion powder, paprika, and dried thyme in a small bowl.
Place the chicken thighs in a large mixing bowl. Add 2 tablespoons of olive oil, Dijon mustard, and the seasoning blend, then toss everything together until the chicken thighs are evenly coated.
Pour the dry rice into a large, oven-safe casserole dish. A casserole dish with a tight-fitting lid is best. If you don't have a lid, you can use aluminum foil.
Add 1 tablespoon of olive oil, 1 teaspoon of kosher salt, the diced onion, and hot water to the rice, then mix to combine.
Place the seasoned chicken thighs on top of the rice in an even layer. It's okay if they overlap a little bit, but try your best to keep them in a single layer.
Cover and bake at 375°F for 40 minutes.
After 40 minutes, remove the dish from the oven, uncover it, and transfer the chicken thighs to a clean plate. Stir the frozen peas and carrots into the rice.
Place the chicken thighs back on the rice, return the dish to the oven, and bake, uncovered, for another 10-15 minutes.
The dish is done when the chicken thighs reach an internal temperature of at least 165°F, the rice has absorbed all of the liquid and is light and fluffy, and the tops of the chicken are lightly golden. Let the dish rest for about 5 minutes before serving, then fluff the rice with a fork, serve, and enjoy!