01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly.
02 - In a large bowl, whisk flour, baking powder, baking soda, salt, and black pepper until blended.
03 - In a separate bowl, whisk together eggs, milk, olive oil, and Greek yogurt until smooth.
04 - Pour wet mixture into dry ingredients and gently stir until just combined, avoiding overmixing.
05 - Incorporate cheddar, feta, red bell pepper, spinach, chives, and sun-dried tomatoes evenly into batter.
06 - Spoon batter into muffin cups, filling each about three-quarters full.
07 - Bake for 22 to 25 minutes until golden and a toothpick inserted in the center comes out clean.
08 - Let muffins cool in tin for 5 minutes, then transfer to a wire rack. Serve warm or at room temperature.