In a small bowl, whisk together the mayonnaise, 2 tablespoons of the sweet n sour sauce (that's ⅛ of a cup), and one clove of garlic.
Blend well and refrigerate until you need it.
Heat olive oil or butter in a skillet over medium-high heat.
Reduce the heat to medium, and add the onions.
Cook until the onions are transparent and soft.
You could stop at this point, but if you have the time, I recommend that you sprinkle the onions with a teaspoon of brown sugar and a few teaspoons of water and allow them to caramelize. Keep them over medium heat (or medium-low if they are drying out), and stir when they look like they're starting to stick, every few minutes. You may have to add a little extra oil or butter. As the onions just start to stick to the pan, they'll turn brown and develop a really sweet, wonderful flavor. Just be careful that they don't burn because there's nothing wonderful about that flavor. This process will take a half hour or so, but it's well worth it if you ask me.
Mix 2 tablespoons of sweet n sour sauce with the onions and keep them warm until the burgers are done.
Mix ground beef together with remaining sweet n sour sauce.
Shape into patties that are slightly larger than the bun (because they'll shrink as they cook).Because our Hawaiian rolls were smaller than normal and oblong, Joe made our patties smaller than normal and oblong, too.
Grill burgers to your preference.
To serve, spread the sweet n sour mayo on the top and bottom of the bun, top with a burger patty, a slice of cheese, a slice of pineapple, and some of those delicious sweet onions.
*Clearly, I forgot to put my onions and pineapple on my burger for the picture. They took the flavor to a whole new level even though they didn't make the photo.