In a medium bowl, mix together the soy sauce (1 tablespoon), garlic powder (1/2 teaspoon), kosher salt (1/2 teaspoon), and black pepper (1/4 teaspoon). Add the diced chicken to the bowl and toss to coat. Allow to marinate for at least 5 minutes.
While the chicken is marinating,mix together all the ingredients for the sweet and sour sauce in a small bowl or glass measuring cup (1/4 cup brown sugar, 1/4 cup honey, 1/4 cup ketchup, 1/4 cup rice vinegar, 1/4 cup water, 1 teaspoon Sriracha, 1 tablespoon soy sauce, and 1 teaspoon garlic powder). This is also a good time to dice the pepper and onion, if you haven't already.
Sprinkle the cornstarch (1/4 cup) on top of the chicken and toss to coat each piece evenly. Use a couple tablespoons more if there isn't enough to coat each piece.
Heat the canola oil (1/4 cup) in a large skillet or wok (I prefer nonstick) over medium-high heat. Add the chicken and fry until crispy and fully cooked, flipping occasionally, about 5-8 minutes. Once fully cooked, remove to a plate.
Add the diced bell pepper, diced red onion (1/2 cup), and diced pineapple (1/2 cup) to the skillet. Sauté over medium-high heat until browned and softened, about 3-5 minutes.
Turn the heat to medium-low and pour the sauce into the skillet. Stir and simmer until sauce has thickened a bit, about 2 minutes.
Add the chicken back into the skillet and stir to coat in the sauce and veggies.
Serve over cooked rice or noodles, or in lettuce wraps for a low-carb version, garnished with sesame seeds and sliced green onions (optional).
For a lighter, lower fat version, you can reduce the oil to 1-2 tablespoons, which will work best with a nonstick skillet.
For a lower-sugar version, reduce brown sugar and honey to 2 tablespoons each.
For 100% gluten-free, be sure to use gluten-free soy sauce.
If you have pineapple juice from dicing the pineapple or from canned pineapple, you can use it in the sauce in place of the water and reduce the sugar by a little bit so it's not wasted.
Ingredient substitutions: chicken thighs may be substituted for breasts; liquid aminos may be substituted for soy sauce; flour, arrowroot powder, or almond flour may be substituted for the cornstarch, yellow, white, or light green and white scallion parts may be substituted for the red onion; fresh minced garlic may be substituted for garlic powder; other Asian-style hot sauce or chili garlic paste may be substituted for Sriracha; white or apple cider vinegar may be substituted for rice vinegar.