To caramelize onions, spray a stainless steel skillet with olive oil spray, add butter and heat on medium until hot.  (You can use a nonstick skillet but the onions won't caramelize as well).

Add onions and cook for about 10 minutes, stirring as needed so they don't burn. Use more olive oil spray if needed. After onions are starting to brown, turn heat to low and continue cooking while you work on the next step stirring occasionally and cooking for another 20 minutes until brown and sticky. 

While waiting for onions to cook, cut chicken breasts and thighs into bite size pieces. Place in freezer for 10 minutes. (When onions are finished, turn off heat and allow to cool.)

After chicken is chilled, place in food processor in 2 batches and chop until chicken is ground (or you can use a meat grinder if you have one).

Place ground chicken in a large bowl. Add garlic, parmesan cheese, salt, pepper and 1/2 c. of the caramelized onions. (Reserve rest of onions to top on burgers). Mix chicken mixture well with hands or spoon.

Use about 1/4 c. of the chicken mixture to make each slider. Place on a baking sheet lined with parchment paper. After forming, chill burgers for at least 20 minutes in the refrigerator. (You can leave them in the refrigerator up to 3 days).

When ready to cook, heat the grill to medium high heat (about 350°). Add the burgers. Cook for at least 5 minutes on one side before flipping the burger. Cook an additional few minutes until temperature of the chicken burger reaches at least 165°. (Or you can pan fry in a nonstick skillet. Fry for 5 minutes before flipping them. Make sure they reach 165° before serving them.

Split Hawaiian rolls in half and place in broiler (or toast for a bit on the grill) until slightly brown. On the bottom half place a chicken slider, top with reserved caramelized onions and 1 T. shredded swiss cheese (if desired).