Preheat your oven to 350°F (≈175°C) and lightly spray a 9 × 13‑inch baking dish with nonstick cooking spray.

In a large skillet over medium‑low heat, cook the bacon until crisp. Remove the bacon and let it drain on paper towels; crumble when cool. Drain away all but about 2 tablespoons of the bacon grease from the skillet.

Return the skillet to medium heat, add the finely‑diced yellow onion and cook for about 5 minutes, stirring occasionally, until the onion becomes translucent.

Add the chopped mushrooms and cook for about 5 minutes more, stirring occasionally, until the mushrooms are golden brown. Then add the minced garlic and cook for 1 minute until fragrant.

Stir in the undiluted cream of mushroom soups. Return the crumbled bacon to the skillet and stir until evenly mixed. Then stir in the milk and the shredded Monterey Jack cheese, and cook until the cheese is melted and the mixture is smooth. Season with salt and pepper to taste.

Gently fold in the drained green beans, making sure everything is thoroughly incorporated.

Pour the mixture into the prepared baking dish. Sprinkle the French fried onions evenly over the top.

Bake uncovered for about 30 minutes, or until the casserole is hot, bubbling, and the topping is golden.

Remove from oven, let it rest briefly (5 minutes) then serve hot.