Preheat oven to 350°F.
Place sliced onions in a single layer on a greased baking sheet. Lightly spray onions with cooking spray. Cook onions until crisp.
In the meantime, bring a large stockpot of water to boil. Add green beans and boil for 3-5 minutes or until soft. Drain.
Heat 2 teaspoons of oil in a large pan over medium-high heat. Add diced onions and mushrooms and sauté, stirring occasionally, for about 10 minutes until soft and cooked.
Add the remaining 2 teaspoons of olive oil and flour and stir.
Add milk, yogurt and seasoning. Let simmer for 5-10 minutes.
Stir in cooked green beans.
Pour into casserole dish, top with baked onions and crushed crackers.
Bake for 30 minutes.
