Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper.

Wilt the spinach quickly in a hot skillet for 20 to 30 seconds or microwave in a covered bowl for 30 seconds. Squeeze out as much moisture as you can and chop if leaves are large.

In a medium bowl, whisk the Greek yogurt and eggs until smooth and uniform.

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

Add the yogurt-and-egg mixture to the dry ingredients. Fold gently just until the batter comes together; a few streaks of flour are fine.

Fold in the squeezed spinach, chopped chives, and shredded cheddar until evenly distributed.

Use a spoon or a 1.5-tablespoon scoop to drop mounds of batter onto the prepared sheet, spacing them about 1 inch apart.

Lightly pat each into a loose biscuit shape.

Bake for 12 to 15 minutes, rotating the pan halfway through, until the tops are golden and a toothpick inserted comes out clean.

Let the biscuits cool on the sheet for 5 minutes, then transfer to a wire rack to cool slightly before serving.