Heat the oven to 350°F (175°C). Grease a standard 9 x 5-inch loaf pan and line it with parchment paper, leaving an overhang on the long sides so the cooled loaf can be lifted out easily.

Whisk the flour, baking powder, baking soda, salt, cinnamon, and optional nutmeg together in a medium bowl until evenly combined.

In a separate large bowl, whisk the eggs, sugar, vegetable oil, and vanilla until smooth. Stir in the lightly drained zucchini.

Add the dry ingredients to the zucchini mixture and stir only until no dry flour remains. Fold in the chopped walnuts or pecans if using.

Beat the softened cream cheese and sugar until smooth. Beat in the egg, vanilla, and flour until the filling is creamy and evenly blended.

Spread about half of the zucchini-bread batter into the prepared pan. Spoon the cheesecake mixture over it, keeping the filling slightly away from the sides, then carefully spread the remaining batter over the top.

Bake for 55 to 70 minutes, until the top is browned and a toothpick inserted into the bread portion comes out with only a few moist crumbs. Do not test directly through the cheesecake center.

Cool the loaf in the pan for 15 to 20 minutes, then lift it out using the parchment and transfer it to a rack. Cool completely, then refrigerate before slicing.