Preheat the oven to 220°C/fan 200°C/gas mark 7. Line a shallow roasting tray (approx 30x20cm) with greaseproof paper.
For the roasted vegetables, mix the potato slices, pepper wedges and onion slices together with the smoky seasoning and olive oil. Arrange everything in a single layer onto the roasting tray. Season to taste with salt and pepper. Roast for 25-30 minutes until the potatoes have softened. Make sure you give everything a careful turn half way through, paying attention not to break the potato slices (don’t worry if a couple do, these can go on the bottom of the omelette!).
In the last 15 minutes of the vegetables roasting, cook the chorizo-style shroomdogs. Place an ovenproof frying pan (approx 30cm in diameter) on a medium heat and add the olive oil. When hot, add the shroomdogs and fry for 8-10 minutes, turning frequently until cooked through.
When ready, remove the shroomdogs from the pan and drain on some kitchen towel before slicing each one diagonally into 4 chunky slices. Remove the pan from the heat for the moment whilst you check the vegetables. Once the vegetables are ready, remove from the oven (but keep the oven on) and put the pan you cooked the shroomdogs in back on a low/medium heat with the oil left from cooking still in.
Arrange most of the vegetables and sausage slices on the bottom of the pan so they are spread out evenly, reserving a handful of the sausage slices and the best looking vegetables. Carefully pour the beaten eggs into the pan making sure not to move everything too much. Season the egg to taste with salt and pepper, then arrange the remaining sausage slices and vegetables evenly on top.
Put the whole pan carefully into the oven and bake for approximately 15 minutes or until the egg has risen and set in the middle. Carefully remove the hot pan, leave to cool for a few minutes or completely before sliding out onto a large plate or board and slicing into large wedges. Scatter over the rocket leaves and serve. This omelette is delicious hot or cold.