This recipe is based on the Cook's Illustrated recipe from their Cover and Bake cookbook. As with all their recipes it is the best. But mine is better :)
Like all casseroles this one freezes well once prepared to just before you put it in the oven.
Melt butter in a large dutch oven over medium heat and cook onions, celery and carrots until soft but not brown. Add garlic, seasoned salt, pepper and chile powders and cook until very fragrant. Add flour and mix well. Cook until starting to color.
Whisk milk and stock into vegetable flour mixture. Turn heat to medium high and continue to whisk as mixture comes to a simmer. Taste and adjust seasoning. Add rice to sauce and lower heat to medium low. Cook until the rice absorbs most of the liquid and is tender, stirring occasionally. Will take about 20 minutes.
Preheat oven to 400 degrees. Add raw chicken to the rice and sauce mixture. Cut green beans into 1 inch lengths and stir into the mixture as well. Cook approximately 4 minutes or until the chicken is no longer pink on the outside. Stir in cheese.
Pour mixture into a 9 x 13 inch casserole, or two 8x8 inch casseroles.
Combine bread crumbs, cheese and garlic powder and sprinkle evenly over top of the casserole. Place in hot oven and cook for 20 to 25 minutes or until topping is browned and casserole is bubbling.
You really should cool for 10 minutes before cutting. You could garnish with parsley and lemon wedges. Or not :).