Preheat oven to 500 degrees F. Warm up a lightly oiled skillet over medium heat. Gently sauté sliced zucchini and squash blossoms to slightly softened. Transfer to a plate until ready to use.
Spread about 1 Tbsp of olive oil in a 12-inch cast iron skillet. Place dough in oiled skillet and gently push and pull dough to fit the bottom of the skillet.
Spread 3 Tbsp pesto on dough, leaving about 1/2-inch border around the pizza. Sprinkle mozzarella and fontina evenly over the pesto. Arrange zucchini and squash blossoms on top. Distribute spoonfuls of ricotta over the pizza. Lightly sprinkle freshly grated nutmeg over pizza. Season with some black pepper.
Transfer skillet to a stove over med-high heat. Warm up the cast-iron and cook pizza dough for about 3 minutes until the bottom of the crust has set and the oil is bubbling along the outer rim of the pizza. In order to have a more defined crust, use a spatula to create an indent around the toppings to separate the crust.
Transfer the hot skillet into the preheated oven. Bake for 8-12 minutes until cheese has melted and is bubbling. Remove from the oven and let sit for 2-4 minutes until unmolding. Place pizza on a cutting board and use a sharp knife or pizza wheel to cut into slices.