Pour the water for cooking the rice into a pot and bring to a boil. 
Wash and trim the zucchini, cut them in half crosswise and hollow them out with a melon baller, making sure to leave about a half-centimeter margin around the edge (is the zucchini open at both ends?). 
Coarsely chop the zucchini flesh with a knife. 
Once the water has come to a boil, add salt and pour in the rice. 
After about 5-6 minutes, add the zucchini pulp and finish cooking the rice according to the times indicated on the package. 
Meanwhile, cut the fontina into cubes. 
When the rice is cooked, stir in the butter and the grated parmigiano with the heat off and mix well.
At this point you are ready to stuff the zucchini: with the help of a teaspoon, fill the hollowed-out zucchini up to halfway, then add a cube of fontina and finish filling it with rice up to the other end. Proceed in the same way with the other zucchini.
Once stuffed, place the zucchini in the pan with the sauce, cover with a lid, and cook over medium heat for about 20-25 minutes. 
After this time, turn off the heat and add a few basil leaves: your rice-stuffed zucchini are ready to serve!

Preparation
To make the rice-stuffed zucchini, start by preparing the sauce: in a pan, sauté the oil with a clove of garlic for 5 minutes, then add the tomato puree, basil, salt, and pepper, and cook for 15 minutes over low heat. After this time, remove the garlic and turn off the heat.