Place the pizza base on a greased baking tray. In a medium bowl, mix together the sour cream, cream cheese and dill until smooth. Spread evenly over the crust.
Heat the olive oil in a frypan over medium heat. Add the onion, mushrooms, garlic and red capsicum; cook and stir until onion is tender but the capsicum is still crisp, about 4 minutes. Stir in baby spinach at the end of cooking. Spread this mixture over the top of the pizza.
Bake for 15 minutes in the preheated oven, or until the crust is golden at the edges. Cut into squares to serve.