Mix dry ingredients: In a large bowl, whisk together the flour, baking soda, sugar, salt, baking powder, paprika, and garlic powder until fully combined.
Combine wet ingredients: In a separate bowl, stir together the buttermilk, melted butter, Dijon mustard, and egg until fully combined.
Combine wet and dry: Make a well in the dry ingredients and pour in the wet mixture. Stir gently until just combined; do not overmix.
Add ham, cheese, and chives: Fold in the diced ham, shredded Gruyere cheese, and chopped chives or scallions until evenly distributed.
Fill muffin tins: Spoon the batter into a muffin tin, filling each cup about three-quarters full as the muffins do not rise much.
Bake: Bake in a preheated oven at 375°F (190°C) for about 25 minutes or until golden brown and set in the middle. Muffins should be firm to the touch.