Slice slider rolls in half horizontally. Spread 1 teaspoon mustard on the bottom of each roll, top with a pickle slice, and set aside.

Heat 2 teaspoons olive oil in a large skillet over medium heat. Add sliced onions to skillet, cook for 1 minute and add the bologna wedges. Cook until onions are tender and translucent, and the bologna is browned on each side, stirring and flipping occasionally, about 3 to 4 minutes.