Fried eggs with spicy onions and spinach

Found this recipe in an aussie magazine, sounded interesting, so I gave it a try...

Butter for frying and spreading, Oil for frying, 4 portobello mushrooms, sliced, 3 onions, sliced, Worcestershire sauce, to taste, Tabasco sauce, to taste, 100g young leaf spinach, Juice ½-1 lemon, 4 large free-range eggs

Put a knob of butter and a drizzle of oil in a large frying pan over a high heat. When the butter is foaming, add the mushrooms and cook for 6-8 minutes until golden brown, stirring regularly. Remove and set aside.

Turn the heat to low, pour a little more oil into the pan, add the onions and cook gently for 10 minutes, stirring occasionally. Increase the heat to medium-high, then cook for 10 minutes more until golden brown. Return the mushrooms to the pan with any resting juices, add Worcestershire sauce and Tabasco sauce to taste, then season with salt and pepper. 

Add the spinach to the pan with the juice of ½ lemon and stir until wilted. Taste and add more lemon juice or seasoning. Using the back of a spoon, make four indentations in the vegetables in the pan and crack an egg into each. Cook for about 3 minutes until the whites are set, then serve with buttered, toasted rolls.