01 - Preheat oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish.
02 - If using fresh green beans, blanch in boiling salted water for 4 to 5 minutes until just tender, then drain. If using frozen green beans, thaw and drain thoroughly.
03 - In a large mixing bowl, add green beans, chopped onion, minced garlic, cream of mushroom soup, whole milk, sour cream, shredded cheddar cheese, Worcestershire sauce, black pepper, and salt. Stir until thoroughly combined.
04 - Spread the green bean mixture evenly into the prepared baking dish.
05 - Evenly sprinkle crispy fried onions over the green bean mixture.
06 - Place tater tots in a single layer, covering the casserole completely.
07 - Transfer baking dish to oven and bake for 40 to 45 minutes until tater tots are golden brown and the filling is bubbling.
08 - Allow casserole to stand for 5 minutes before serving.