Make the toasts 1 day ahead. Preheat oven to 400 degrees F.
Take 8 slices white bread and cut out 32 circles using a 1 3/4-inch round pastry cutter or an empty, clean 6-ounce tomato paste can. Arrange discs on an unlined sheet pan and spray lightly with olive oil. Toast rounds for 7 minutes. When cool, store in an airtight container.
Make the burgers the day of. Preheat oven to 400 degrees F.
Mix ground beef, seasoning, egg, and Worcestershire sauce in a large bowl. Form 1-inch meatballs using 1 tablespoon of meat mixture per ball. Arrange on a broiling pan, leaving an inch space between meatballs. Using index finger, gently poke holes in the middle of each meatball. Bake for 12 minutes. Turn temperature to broil and cook for another 5 minutes. Let stand 7 minutes before transferring to toasts.
Gently fill each burger hole with ketchup or mustard. Serve warm.