Finely grate the cheese. Unroll the pizza dough and place it on a baking tray with baking paper. (Process immediately). Sprinkle cheese evenly on the dough and bake in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see manufacturer) for 15-20 minutes.
In the meantime peel and halve the onions and cut them into strips. Clean, wash, quarter, seed and dice the tomatoes. Cut avocados in half, remove the core, remove the flesh from the skin and dice. Mix with lemon juice.
Pour sour cream into a piping bag with a small perforated spout. Take the pizza out of the oven and sprinkle with onions. Cover with tomatoes. Season with salt and pepper. Spread avocados on top. Spray sour cream in strips evenly on top. Cut into pieces and serve.