Preheat the oven to 200 degrees F.
In a large bowl, combine the zucchini, onions, basil, zest, garlic, salt, and pepper. In a small bowl, combine the flour and baking powder. Add the eggs and flour mixture to the vegetables and stir just until combined.
Heat a large, nonstick skillet over medium-high heat for 3 minutes. When hot, add enough oil to coat the bottom of the pan. Add the batter by tablespoons into the skillet (making sure to spoon both batter and vegetables), leaving 1-inch between the cakes. Immediately drop a round of cheese into the center of each pancake. Top with another tablespoon of batter to enclose the cheese. Cook until golden brown on the bottom side, about 1 1/2 minutes. Flip with a spatula and cook on the 2nd side until golden brown, about 1 minute. Remove from the pan and place on a baking sheet. Keep warm in the oven while preparing the remaining pancakes.
Arrange the pancakes on a platter, drizzle with the tomato sauce, and serve immediately.
Yield: 4 to 6 servings (about 24 small pancakes)