Heat ¼ cup olive oil in a 2 quart saucepan over low heat.
Add in the onion and saute slowly until soft.
Add in the zucchini and garlic, briefly saute over medium heat until the garlic gives off it aroma.
Heat the broth in another pan until it is very hot; turn off the heat, but keep the broth hot.
Add the rice to the zucchini mixture and, stirring constantly with a wooden spoon, saute until the rice is opaque and makes a clicking sound against the metal of the saucepan, approximately 1-2 minutes.
Add the hot broth to the rice one ladleful at a time, stirring frequently.
The rice should cook very slowly over low heat.
Wait until the liquid is absorbed before adding the next ladleful of broth.
Midway in the cooking time, add the basil and salt and pepper to taste.
When the risotto is al dente, add the mozzarella, the remaining 2 tablespoons olive oil, and the parmesan cheese.
Turn off the heat and stir vigorously until all the oil and cheese are absorbed; serve immediately.