1) Preheat the oven to 200C/Gas 6.
2) Put the oil and onions in a medium skillet and cook over very low heat, stirring occasionally, until onions are soft and caramelised, about 15 mins. Turn the heat up to medium and add the rocket. Cook until the rocket is wilted, about 1 min. Season with salt and pepper.
3) Place the tortillas on a baking sheet and top each with some of the rocket/onion mixture. Crumble some goat cheese on top of each, and bake for 10 mins. Allow to cool for a few minutes and cut each pizza into 4 triangles.