Put spring mix in large salad bowl.
In a skillet over medium heat, add the olive oil. Add bacon and cook slowly until bacon begins to brown, 5-10 minutes. If you prefer your bacon crispy, continue to cook until bacon is crispy.
For poaching: While bacon is browning, bring a small pot of water and 2 tablespoons of white vinegar to a gentle boil.
Back to the skillet: once bacon is hot and at your desired crispiness, add shallot or onion and cook until softened, a minute or two. Add the Sherry or Cider vinegar and mustard to the skillet and turn heat to lowest setting.
To poach eggs: In gentle water boil, slowly pour each egg into the bubbling water. Cook eggs for 3 to 5 minutes, just until the white is set and the yolk has filmed over. Remove each egg with a slotted spoon and drain briefly on paper towel.