1. Preheat your oven to 400 °F and heat a large skillet over medium-high heat.
2. Once the skillet is hot, add in ½ tablespoon of olive oil and the chicken, cooking for 3 to 5 minutes.
3. After that time, remove the chicken from the skillet, set it aside, return the skillet to the stove, and lower the temperature to medium heat.
4. Once the skillet is hot again, add in the last ½ tablespoon of olive oil and all the onions, sautéing for 3 to 5 minutes.
5. After that time, add in mushrooms and garlic, and let sauté for 5 to 8 minutes.
6. After that time, remove the skillet from heat and set it aside with the veggies.
7. Grease a large baking dish with the cooking spray, then whisk together the rice, water, and soup in the dish.
8. Once fully combined, add in the chicken and vegetables, stirring everything together.
9. Once the dish is fully combined, cover it with aluminum foil, place it in the oven, and bake for 45 minutes.
10. After that time, remove the foil, add the shredded cheese, and bake for another 5 to 20 minutes uncovered, until all the liquid is absorbed and the cheese is melted.
11. Once the casserole has absorbed all liquid and the cheese has melted, remove it from the oven, let it cool for a few minutes, and then serve it up!
