Heat a skillet over medium heat, and once hot, add the oil to the pan. Add the onions and sauté for about 2 minutes, stirring while they soften. Add the tomatoes, Cajun seasoning, and chicken, then stir and cook for another minute.
Add the white rice and stir to combine with everything in the pan. Pour the chicken broth (or water) into the skillet, stir, and bring everything to a boil.
Once it's boiling, add the frozen mixed veggies and stir everything. Bring it back to a simmer, then reduce the heat to the lowest setting or transfer to a smaller burner. You'll want to cook the rice over the lowest heat possible while you still see the liquid simmering. Too hot and the rice will stick. If your burners are large, check after 10 minutes that the rice isn't stuck to the bottom.
Cover with a lid and cook until the rice is soft, for about 20 minutes. Turn off the heat, remove the lid, and let the chicken and rice sit for 5 minutes. Evaporating any excess water helps prevent mushy rice.
Serve:
Before serving, fluff the rice with a fork, then spoon into bowls.
Notes
No Cajun seasoning? Use Creole seasoning or a blend of 2 teaspoons paprika and 1 ½ teaspoons garlic powder, 1 ½ teaspoons onion powder, 1 teaspoon oregano, 1 ½ teaspoons salt, and a pinch of cayenne.
Use broth for more flavor. Chicken broth gives the rice a richer taste, but water works too. If using water, add 1 ½ teaspoons salt.
Swap the vegetables. Frozen peas, corn, green beans, broccoli, carrots, or your favorite frozen vegetable blend all work well.
Use long-grain white rice. Brown rice will require 45 minutes of cooking and a little extra water (check the ratios on the back of your bag).