Prepare the green beans: Trim and cut 1 lb. fresh green beans into bite-sized pieces. Place them in an 8" baking dish or a 7" bucket-style baking pan that fits your air fryer. Spray the green beans lightly with oil.
First Air Fry: Place the dish in your air fryer and cook at 340°F (170°C) for 12 minutes. Stir halfway through for even cooking, or stir 3 times during the 12 minutes until the beans reach your desired tenderness.
Make the creamy sauce: In a bowl, whisk together 14 oz. cream of mushroom soup, 1/2 cup milk, 1 Tablespoon Worcestershire sauce, 1/2 teaspoon garlic powder, and 1/4 teaspoon black pepper. Taste and add salt if needed.
Combine and second Air Fry: Pour the sauce over the air-fried green beans and gently stir to coat. Place the dish back into the air fryer and cook at 340°F (170°C) for 11-13 minutes, stirring halfway through, until the sauce is bubbly and the beans are tender.
Add the crunch: Top the casserole with 1 cup of fried onions and 1/4 cup of shredded cheese (if using). Air fry for an additional 1-2 minutes at 340°F (170°C), or until the cheese is melted and bubbly.