Preheat the oven to 350 degrees F. While the oven is heating up, start cooking the white rice. I try to make a little more than I actually need in case I need to add more. Put 2 cups rice and 3 cups water into a medium pot on high heat, cover and bring to boil. Once it boils over a little, stir it, reduce heat to low and put lid back on only let it cook on low for about 3-4 minutes and remove from heat but keep covered for about 20 minutes.
On the stovetop heat a large pan to medium and then add oil and allow to heat for less than a minute. I used cooked chicken but if you have to cook your chicken then cook it now and let it set before cutting in cubes. If you already have cooked chicken then now you will add the onion, bell pepper, celery and carrots and cook until tender, about 7-10 minutes.
In a large bowl, mix together the cans of soup, sour cream, rice, chicken and cooked vegetables. I put these in two separate 9x9 dishes so I have one to eat now and one to freeze but you can pour all of the mixture into a 9x13. Cover and put in the oven and cook for 25 minutes. While casserole is cooking, run the crackers through a food processor or crush them. Melt the butter and mix with crushed crackers in a medium bowl.
Remove the casserole and uncover. Add the cracker mixture on top spreading it evenly and return uncovered to oven for 10-15 minutes.