In a large pan over medium heat, cook bacon until crispy.
Transfer the cooked bacon to a paper towel-lined plate and crumble it into pieces.
In a small mixing bowl, mix together the shredded cheeses.
Mix together sour cream, cream cheese, mayonnaise, and spices. Fold in the steamed vegetables, half of the crumbled bacon, and ~1 cup of your shredded cheese mixture. Transfer that to your baking pan and spread into an even layer. Sprinkle the remaining shredded cheese and bacon crumbles on top.
Cover the pan with foil and bake. Then, remove the foil, move your oven rack to the top rack and turn on the broiler. Broil the casserole until the cheese on top is bubbly and golden.
Remove the pan from the oven and allow the casserole to cool slightly before garnishing with chopped green onions.