Preheat the oven to 350 degrees F. Lightly spray a 9-by-5-by-3-inch metal loaf pan with nonstick cooking spray and set aside.
In a medium bowl, whisk the flour, baking powder, baking soda, 3/4 teaspoon dry mustard, kosher salt and cayenne until combined. In a large bowl, whisk together 3/4 cup milk, the oil, 1 tablespoon honey and the eggs until smooth. Stir in the dry ingredients until just combined. Then fold in the ham, 3/4 cup shredded cheese, the diced cheese and scallions.
Pour the batter into the prepared loaf pan and sprinkle the top with the remaining 1/4 cup shredded cheese. Bake until well risen, golden brown and a skewer or cake tester inserted in the center comes out clean, 40 to 45 minutes.
Cool in the pan for 10 minutes. Meanwhile, in a small microwave-safe bowl, stir together the remaining 1 tablespoon each honey and milk and the remaining 1 1/2 teaspoons dry mustard until smooth. Heat in the microwave until hot and bubbling, 20 to 30 seconds. Turn the loaf onto a wire rack and generously brush with the warm glaze. Cool completely.