Preheat your oven to 375°F (190°C) and prepare a 12-cup muffin tin by greasing it lightly or using muffin liners.

In a large mixing bowl, whisk together the all-purpose flour, ground flaxseed, baking powder, salt, garlic powder, and red pepper flakes.

In a separate bowl, beat together the Greek yogurt and large eggs until smooth.

Gently fold the wet mixture into the dry ingredients using a spatula until just combined, being careful not to overmix.

Stir in the wilted spinach, chopped chives, and shredded cheddar cheese until evenly incorporated.

Divide the biscuit mixture among the prepared muffin cups, filling them about three-quarters full.

Bake for 20-22 minutes until golden brown and a toothpick inserted into the center comes out clean.

Allow to cool slightly in the tin for about 5 minutes before transferring to a wire rack to cool completely.