Preheat the over to 400 degrees Fahrenheit. Line a medium baking tray with parchment paper or spray with oil.
In a medium bowl mix together ground chicken, diced red pepper, drained and pressed crushed pineapple, panko breadcrumbs, scallion, garlic, ginger, salt and pepper. Use a spoon or your hands.
Divide the mixture into 22 parts (I used a medium cookie scoop) and roll uinto meatballs using wet hands. Place the meatballs on the prepared baking tray.
Bake in preheated oven for 20-25 minutes. If you want, you can spray the meatballs with some oil before baking (to help them brown), though it's not necessary.
While the meatballs are baking, prepare the Teriyaki Sauce. In a bowl or a measuring cup whisk together reserved pineapple juice, ½ cup water, soy sauce, sugar, garlic and ginger.
In a small bowl mix 1 ½ tablespoon corn starch with 2 tablespoons cold water until dissolved. Set aside.
Pour the soy sauce pineapple juice mixture into a medium or large skillet and cook, whisking over medium heat, until sugar dissolves.
Add the starch slurry and keep stirring (I use a silicone whisk) until the sauce thickens.
Once the meatballs are baked, transfer them to the skillet with Teriyaki Sauce and toss to coat.
Serve immediately garnished with sliced green onions and toasted sesame seeds.