Toss pork pieces with cornstarch until lightly coated.
Heat oil in a large skillet over medium-high heat.
Add pork and cook until browned on the edges, about 4–5 minutes.
Add bell peppers and cook 2 minutes until slightly tender.
In a bowl, whisk together ketchup, vinegar, pineapple juice, honey, soy sauce, ginger, and garlic.
Pour sauce into the skillet and stir.
Simmer 2–3 minutes.
Add the cornstarch slurry and stir until the sauce thickens.
Fold in pineapple chunks.
Serve over rice and garnish with green onions or sesame seeds.