Make the aioli. Whisk together mayonnaise, garlic, and lemon juice. Season to taste with salt and pepper.
Toast the buns. Preheat oven to 400°F or 204°C. Place rolls, cut sides up, on a baking sheet. Bake 6-8 minutes or until lightly toasted.
Fry the bologna. Heat a large skillet over medium heat 1 minute or until hot. Add bologna, and fry 2-3 minutes on each side or until browned. Drain on paper towels.
Assemble sliders. Spread aioli generously on the inside of the bun tops. Spread mustard on the inside of the bun bottoms. Layer bologna and fried onions on roll bottoms. Cover with roll tops, and serve.