If you’re going with this odd but beloved dish, which involves fat- and sodium-filled canned soup and french-fried onions, swap the soup for a from-scratch sauce and the fried onions for caramelized ones (or baked Lay’s potato chips).
“Green beans are loaded with fiber and vitamin C,” says Miranda Hammer, “and should occupy a lot of the real estate on your plate.”
Miranda Hammer, R.D. is a registered dietitian based in New York City
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Ingredients 

1 1/2 lbs fresh green beans, trimmed and halved crosswise
2 Tbsp butter, separated
2 onions, peeled and thinly sliced
Salt
8 oz mushrooms, chopped coarsely
1 onion, chopped coarsely
2 garlic cloves, minced
1 cup chicken stock
1 cup milk
3 Tbsp flour

How to make it 

Bring a pot of salted water to a boil, add green beans, cook for 5 minutes, then drain and cool.

Melt 1 Tbsp butter in a pan over medium heat, add sliced onions, salt lightly, and cook until onions are browned. Preheat oven to 400°. In a large pan, add mushrooms, chopped onion, garlic, and 1 tsp salt; cook for 10 minutes over medium heat.

In a separate saucepan, bring stock and milk to a simmer; add flour and cook, stirring constantly, for about 2 minutes. Add stock mixture to mushrooms; bring to a boil, stirring until thick.

Put beans in a baking dish, add mushroom mixture, and top with the caramelized onions; cook for 15 minutes.

Lightened-up recipes

https://www.mensfitness.com/nutrition/healthy-recipes/better-grandmas-green-bean-casserole