Healthy Green Bean Casserole

INGREDIENTS

2 1/2 lb

green beans, trimmed and cut into 1- to 2-inch pieces (about 8 cups)

2 tbsp

olive oil, divided

1 tbsp

flour

red onion, thinly sliced

4 oz

mushrooms, minced very finely

3/4 tsp

Kosher salt

1/4 tsp

black pepper

2 1/2 cups

2% milk

1 cup

50% fat sharp cheddar cheese, shredded