Place the flour, yeast and teaspoon of salt in a food processor fitted with a dough attachment (or use a bowl and a wooden spoon if you don’t have a processor). Mix the oil and warm water in a jug. With the motor running, slowly pour in the oil mixture through the feeder tube; or stir by hand and mix until you have achieved a soft, stretchy dough. Knead for 5 minutes in the machine or for 10 minutes by hand on a lightly floured work surface.
Transfer the dough to a lightly oiled bowl, rub the top with a little more oil and then cover with a clean, damp tea towel. Set aside at room temperature for 1 hour or until the dough has doubled in size.
To prepare the toppings, put the sugar and vinegar in a small pan and bring to simmer until the sugar has dissolved. Remove from the heat and add the red onion slices. Season to taste and set aside to allow the flavours to combine.
Heat some olive oil in a heavy-based frying pan and cook the rump steak over a high heat for 5 minutes on each side until just rare. Remove from the heat and leave to rest in a warm plate. Add a little more olive oil to the pan and sauté the pumpkin for 8-10 minutes until the pumpkin is cooked through but still holding its shape. Set aside until needed.
Preheat the oven to 240°C/475°F/Gas Mark 9. Punch the dough down, with a clenched fist. Remove the dough from the bowl and knead for a couple of minutes until smooth, then cut in half and roll each half out on a lightly floured surface to a very thin large rectangle. Sprinkle the semolina or breadcrumbs on to two large, flat baking sheets and transfer the pizza bases on top.
Drizzle with olive oil and arrange the sautéed pumpkin and Cashel blue on the pizzas. Bake for 8-12 minutes until the base is crisp and Cashel blue cheese has melted. Cut the rested beef into thin slices. Remove the pizza from the oven and add mounds of the sweet pickled red onions. Scatter over the rocket and then drape over slices of the rare roast beef to serve.