01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or grease thoroughly.
02 - In a large bowl, whisk together all-purpose flour, baking powder, baking soda, salt, and black pepper.
03 - Add shredded cheddar, crumbled feta, diced bell pepper, chopped spinach, and chives to the dry mixture. Toss gently to coat evenly.
04 - In a separate bowl, whisk eggs, whole milk, olive oil, and plain Greek yogurt until smooth.
05 - Pour the wet ingredients into the dry ingredients bowl. Stir gently until just combined, ensuring not to overmix.
06 - Divide the batter evenly into muffin cups, filling each about three-quarters full.
07 - Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean.
08 - Let muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely or serve warm.