Bake the sweet potato (yam) for 45-60 mins on 200 degrees°C (392 °F) or until completely soft.
While the sweet potato (yam) is baking, you're going to make the Basil Pesto (recipe below)
Separately cut your Tempeh into triangle pieces and then turn side on and cut so the pieces are thin. Next, lightly pan fry or bake the chopped onion and then the Tempeh for 10 minutes and turn at halfway point. Usually I would bake the tempeh for 15 minutes, but as you are going to cook the pizza again later they can be slightly undercooked at this point. You can season these with your favourite spices before baking (cumin, paprika, cayenne pepper, turmeric, etc).
Once the sweet potato (yam) is ready, remove the skin, mash and add in your favourite spices, salt and pepper.
Spread the Pesto across your vegan pizza base and then the sweet potato (yam). Then, layer the onion, rocket, tempeh.
Place in the preheated oven on 200 degrees°C (392 °F) until the pizza is warm/crispy and cheese softens.