For the fried potatoes, cut the potatoes into quarters and put in a medium saucepan. Cover with water and bring to the boil. Reduce the heat slightly and cook for 10–15 minutes, or until tender. Drain well in a colander, tip back into the pan and toss around a bit to break up the edges.
For the fry up, preheat the oven to 200C/180C Fan/Gas 6. Put the sausages, if using, and tomato halves on a lightly oiled baking tray. Season the tomatoes with flaked sea salt and ground black pepper and bake for 12–15 minutes, or until the sausages are lightly browned and hot throughout.
Meanwhile, to continue the fried potatoes, heat two tablespoons of oil in a medium non-stick saucepan pan and fry the potatoes, red onion, a good pinch of salt and lots of ground black pepper for 8-10 minutes, or until lightly browned and crisped in places, turning regularly.
To finish the fry up, heat one tablespoon of oil in a large non-stick frying pan and fry the mushrooms for 2–3 minutes over a high heat until lightly browned, stirring regularly. Season well, add the spinach and toss together for 30–60 seconds, or until the spinach wilts. Push the mushrooms and spinach to one side of the pan and reduce the heat.
Break the eggs into the pan and cook for 2–3 minutes, or until the whites are set but the yolks remain runny.
Meanwhile, toss the potatoes with the chopped fresh rosemary or thyme, and chilli (if using), and cook for a few seconds more.
Spoon the potatoes onto two plates, add the sausages, tomatoes and mushrooms and place the fried eggs alongside.