Preheat oven at 180ºC / 350ºF. Grease muffin cups.
Cook bacon in a skillet over medium heat until crisp. Drain on paper towel.
In a large bowl, mix flour, baking powder and baking soda. In another bowl, mix milk, vinegar, salt, yogurt, oil and egg. Gradually, pour the liquid ingredients into the dry ingredients and mix. Then add the onion, bacon and cheese, and mix to combine. Fill each muffin cup with a large tablespoon of the batter and sprinkle each one with more Cheddar cheese (optional). Bake for 20-25 minutes or until golden. Serve warm or at room temperature.