Cut bacon into small pieces and sauté until cooked. Once cooled, set aside 1/4 of the bacon for the topping.
In a bowl, add 3/4 of the bacon, 1/4 cup sour cream, 16 oz cream cheese, 1/2 cup four-cheese blend, 1 cup cheddar cheese, 3 Tbsp green onions, 1/4 cup walnuts, 3 Tbsp Ranch seasoning, 1/2 tsp garlic powder, 1/4 tsp pepper, and 1 tsp poppy seeds. With a wooden spatula, mix all ingredients until well combined.
Finely chop the remaining 1/4 of bacon, 1/4 cup cheddar cheese, 1 Tbsp green onion, and 1/4 cup walnuts. Mix together with the 1/4 tsp poppy seed. Spread this mixture onto a cutting board.
Form a ball out of the cheese mixture and roll the cheese ball over the toppings to fully coat and shape into an even ball as it's coated. Serve right away or cover and refrigerate until ready to serve.