Preheat the oven to 375 degrees and lightly grease a 12-cup muffin tin.
In a large bowl, combine the ground beef, panko breadcrumbs, egg, 1/4 cup teriyaki sauce, diced pineapple, minced onion, garlic, salt, and black pepper.
Mix the ingredients with your hands until evenly combined but do not overwork the meat.
Divide the mixture evenly among the muffin cups, pressing it down gently to fill each cup.
Brush the tops of each muffin with the remaining 2 tablespoons of teriyaki sauce.
Bake for 22 to 25 minutes until the internal temperature reaches 160 degrees.
Remove from the oven and let the muffins rest in the tin for 5 minutes before removing.
Sprinkle with chopped green onions before serving.