Bring a medium pot of water to a boil.
Meanwhile, crack your egg into a small mesh strainer and let the whispy part of the egg whites fall through. Discard it, or save it to use in another recipe later. Transfer the egg to a small ramekin or bowl.
Once the water is almost boiling, add in the vinegar. When it's boiling, turn the heat to low and gently drop the egg into the water. Let the egg cook for 3 minutes.
While the egg is cooking, pop a slice of bread into the toaster. Also, mix together the harissa, tahini and lemon juice in a small bowl.
Remove the egg with a slotted spoon and place it onto a plate lined with paper towel to absorb the extra water.
Assemble the toast. Start by spreading a thick layer of yogurt over the bread. Then add arugula, poached egg, a drizzle of harissa tahini sauce and honey. Season with salt and pepper.