Place the cornstarch, beat eggs and panko in three seperate bowls for breading.
Begin dredging your chicken with the cornstarch first, then egg and lastly the breadcrumbs. Place the breaded chicken cubes on a plate until all are completed.
Combine the brown sugar, soy sauce, vinegar, ketchup, and pineapple juice in a bowl or large measuring cup and stir to combine.
Heat the oil in a large saute pan or skillet over medium heat. When the oil is hot (about 350°F), begin frying the chicken. Cook for 5 minutes, or until golden brown, flipping once halfway through the cook time. Working in batches to not crowd the pan.
Remove the cooked chicken to a sheet pan lined with a cooling rack to drain.
Pour off all but 1 tablespoon of oil and remove as much excess breadcrumb from the pan as possible.
Add the onions and peppers and saute until tender and the onions are beginning to caramelize.
Add the pineapple chunks and garlic to the pan and stir, cooking for about 30 seconds to one minute.
Pour sauce over the peppers and stir until the sauce is smooth and beginning to bubble.
Reduce heat to low and let simmer until it thickens slightly, approximately 2 minutes, then return the chicken to the pan and toss it all to combine. Serve immediately.
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