Start by adding the soy sauce, tomato paste, Worcestershire sauce, garlic powder, brown sugar, and black pepper straight into the crockpot. Stir it all together until it looks like a smooth, glossy sauce. This forms the backbone of flavor for everything that goes in next.
Add your cubed chicken, diced red bell pepper, and the full can of pineapple chunks, juice included, right into the pot. That pineapple juice is doing double duty here, adding sweetness and helping tenderize the chicken as it cooks.
Give everything a gentle stir so the chicken and peppers are evenly coated in that sauce. You don't need to overdo it, just make sure nothing is sitting dry at the bottom or piled up out of the liquid.
Cover the crockpot and set it to low for 4-6 hours, or high for 2-3 hours if you're short on time. Low and slow is the better route whenever your schedule allows for it, since the flavors have more time to develop.
About 30 minutes before you plan to eat, lift the lid and taste the sauce. If it needs more punch, stir in a little extra soy sauce or brown sugar until it tastes right to you.
Once it's done, scatter some sliced scallions over the top if you like, and spoon it over a bed of rice. That's it, dinner is ready.