You can use all butter or all olive oil if preferred. You can use fresh rosemary instead of dried, and green bell pepper instead of poblano.
You can brown the hash for as long as you'd like. I go for severe "crustification" which I believe improves the taste and texture.
To turn this into cheeseburger hash, stir in a nice big handful of sharp Cheddar cheese when you add the green onions.