Heat the avocado oil in a large skillet over medium heat and add the chopped onion, Sauté, stirring occasionally, until the onion has softened, about 3 minutes. Add in the chopped apple and minced garlic and continue sautéing until the garlic is fragrant and the apple has softened slightly, about 3 to 5 minutes. Remove this apple mixture from the heat and stir in the pure maple syrup, celery powder (if adding), ground cinnamon, and sea salt. Set aside to cool for 10 minutes.

Once the onion and apple mixture has cooled, transfer the ground chicken to a large bowl along with the mixture. Use your hands to mash everything together until the onion and apples are well distributed throughout the ground chicken.

Form patties out of the chicken mixture, making any size sausage patties you like.

Place a cast iron skillet on the stove top and add enough avocado oil to generously coat the surface (about 3 tablespoons). Heat to medium high heat and allow the skillet to heat for a few minutes.

Carefully place the chicken sausage patties on the hot skillet in a single layer, giving them a little space in between. Cook for 3 to 4 minutes, then flip to the other side and cook for another 3 to 4 minutes, about 8-10 minutes total. Continue cooking and flipping until the patties reach an internal temperature of 165 degrees fahrenheit. To check for doneness, insert a digital thermometer into the center of a patty.