Preheat oven. In a saucepan, heat up 1 tbsp of olive oil and add mushrooms, bell pepper and onions. Saute until soft and mushrooms begin to caramelize. Season with salt and pepper. Set aside Now, prepare your pizza sauce. Using a potato masher or fork, mash tomatoes until saucy, then add salt and pepper. (Non-vegetarians: you can also mash 1-2 anchovy fillets and add to the sauce to give it a real salty boost.)
Preheat oven (follow instructions on your pizza box).
Spread a thin layer of olive oil on your pizza crust. Now, spread your pizza sauce on top.
(Optional) Over the sauce, I like to sprinkle a layer of grated parmesan cheese. You can skip this step but it adds a nice layer of savouriness to the mixture.
Now, layer your cooked vegetables on top.
Over this, scatter the basil leaves. Basil leaves are delicate so if you lay them on top of everything, exposed directly to the high oven heat, they will burn and you don't want that!
The last ingredient to go on should be shredded cheese. Try to include mozzarella as it will give it the cheese pull effect. Don't be stingy with your cheese - nothing worse than a pizza with insufficient cheese!
Pop into pre-heated oven and bake until cheese is golden and bubbly. Serve!