Preheat a grill pan or a large nonstick skillet over medium high heat or, preheat outdoor grill.
Combine the meat with onion, Worcestershire and steak seasoning or salt and pepper. Form 2-inch meatballs, then flatten them into patties. Drizzle formed mini patties with extra-virgin olive oil to keep them from sticking to cooking surface.
Slice the brick of cheese into 1/4-inch pieces. Place patties into a preheated pan or grill pan or arrange on outdoor grill. Cook the mini burgers for 3 minutes on each side then add cheese to melt over patties. On outdoor grill, close the lid to melt cheese. In a skillet or on a grill pan, tent the mini cheeseburgers loosely with foil to melt cheese.
Coarsely chop romaine and combine with sliced pickles and halved cherry or grape tomatoes.
Whisk together the mustard and cider vinegar. Stream in the extra-virgin olive oil. Add the chopped chives and pimentos, stir to combine
Arrange mini cheeseburgers on salad and drizzle prepared yellow mustard over the completed dish.
*There are many flavors of sharp Cheddar out in today's markets to choose from, so go plain or go wild! Among the choices out there in sharp cheddars: 5-peppercorn, smoked, dill, garlic and herb, roasted garlic, horseradish, chipotle, habanero, jalapeno –on and on!