Begin by making the hollandaise. Melt the butter using whatever method you prefer. While it's still hot place the avocado, lemon juice, egg yolk and salt and pepper in a small food processor and process until smooth. With the motor running slowly add the butter in a thin stream until thick. Decant into a jug and cover with cling film while you cook the mushrooms.
Use a mandolin to finely slice the mushrooms, around 2-3 mm thick. Combine the oil, soy, sugar and smoked paprika in a flat based dish. Stir well and add the mushrooms and gently toss to coat. While the mushrooms are marinating place a frying pan over a medium high heat. Once the pan has heated add the extra oil and fry the mushroom mushroom, in a single layer (you may need to cook in more than one batch) for 1 minute, before turning and frying for a further minute or until golden brown. Drain on paper towel.
To assemble the final dish place slices of the mushroom "bacon" on the toasted muffins or toast and top with a poached egg. Finally drizzle with the avocado hollandaise, avocado slices and serve immediately.