Preheat your oven to 375°F (190°C) and grease a muffin tin or line it with paper liners.
In a large bowl, combine the flour, baking powder, salt, black pepper, garlic powder, and onion powder. Mix well.
In another bowl, whisk together the milk, eggs, and olive oil until well combined.
Add the wet ingredients to the dry ingredients and stir until just combined. Do not overmix.
Gently fold in the chopped spinach and crumbled feta cheese until evenly distributed.
Divide the batter evenly among the muffin cups, filling each about ¾ full.
Bake in the preheated oven for 20-25 minutes, or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.