Need healthy green bean casserole recipe

It depends on your definition of healthy and tasty.

If I was going for lower calorie I would start with fresh green beans, onions and mushrooms roasted at a high temp to bring out some flavor. (Different roasting times - green beans a few minutes, mushrooms more, onions longest) For the creamy portion use a combination fat free creamy soup, FF sour cream and/or Greek yogurt. Add lots of seasonings of your preference, depending on how traditional you want it (salt, pepper, Rosemary, thyme, sage, celery salt, garlic powder, etc... ). For the crunchy element just top with less of the fried onions or serve them on the side. Don't stir any into the casserole - the roasted onions will work in the casserole.