To Poach Eggs: Add enough water to the pot or pan to fill half full of water. Add vinegar. Bring to boiling; reduce heat to simmering (bubbles should begin to break the surface of the water). Break one egg at a time into a measuring cup. Holding the lip of the cup as close to the water as possible, carefully slip egg into simmering water. Repeat with an additional egg. Leave some space between each. Simmer eggs, uncovered, for 3 minutes or until the whites are completely set and yolks begin to thicken a bit but are not hard. Using a slotted spoon, carefully remove eggs from a plate.
In the meantime, preheat oven to 400 degrees. Toast English muffin halves and set aside. Spread the cut side of each muffin half with ½ of the cheese wedge. Place muffin halves, cheese side up, in prepared dish. Top each with the ham pieces. Place tomato slice or slices on top. Add a cooked egg to each.
To Make Hollandaise Sauce: In a small bowl, mix together yogurt, mayonnaise, mustard, butter, and a little salt and pepper. Divide and spoon Hollandaise Sauce over eggs. Spread over top using the back of the spoon.
Cover pan with foil and bake for about 10-12 minutes until heated through.
Serve at once with a fork and knife.