Preheat the oven to 350°F (175°C) and lightly spray a 9x13-inch baking dish with nonstick cooking spray.

In a large skillet over medium-low heat, cook the bacon strips until crisp. Remove the bacon, drain on paper towels, and crumble it into small pieces. Drain all but 2 tablespoons of the bacon grease from the skillet, return it to medium heat, and add the diced onions. Cook for about 5 minutes until the onions become translucent.

Add the chopped mushrooms to the skillet with the onions. Cook for about 5 minutes until the mushrooms turn golden brown. Add the minced garlic and cook for about 1 minute until fragrant.

Stir in both cans of cream of mushroom soup without diluting. Add the crumbled bacon back into the skillet. Stir in the milk and shredded Monterey Jack cheese until the cheese melts completely and the mixture is smooth. Season with salt and pepper to taste.

Fold in the drained green beans gently to ensure they are well coated with the creamy mushroom mixture.

Pour the green bean mixture into the prepared baking dish. Evenly spread the French fried onions on top. Bake uncovered in the preheated oven for 30 minutes or until the casserole is hot, bubbly, and the topping is golden.