Preheat: Preheat your oven to 375°F (190°C). Grease and flour one 9x5 inch loaf pan or two smaller loaf pans.
Cream: In a large bowl, beat the softened cream cheese and butter together until smooth and creamy.
Mix: Gradually add the sugar to the cream cheese mixture, beating well after each addition. Beat in the eggs one at a time, then stir in the lemon zest.
Whisk: In a separate bowl, whisk together the flour, salt, baking powder, and cinnamon (if using).
Combine: Gradually add the dry ingredients to the wet ingredients, alternating with the milk, and mixing until just combined. Do not overmix.
Fold: Gently fold in the diced peaches.
Bake: Pour the batter into the prepared loaf pan(s). Bake for 50-55 minutes for a large loaf or 45-50 minutes for smaller loaves, or until a toothpick inserted into the center comes out clean.
Cool: Let the loaf cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.