Combine onion, fresh pineapple chunks, soy sauce, rice wine vinegar, honey, sesame oil, garlic, five-spice powder, bell pepper, jalapeno pepper, and peanut butter in a 5 or 6-quart slow cooker crock.
Heat olive oil in a large skillet over medium-high heat. Season trimmed pork roast on all sides with salt and pepper, to taste. Sear roast on all sides, approximately 2-3 minutes per side. Transfer seared pork to slow cooker crock.
Reduce heat in skillet to medium and add the fresh pineapple juice. Use a spatula to scrape up flavorful brown bits from bottom of pan. Remove from heat and pour pan juices into the slow cooker.
Cover and cook over high heat for 3-4 hours or low for 6-8.
Stir in fresh cilantro and transfer pork and pineapple mixture to a serving platter with a slotted spoon.
Combine 2 tablespoons cornstarch (arrowroot) and ¼ cup of juices from the slow cooker. Pour remaining juices from the slow cooker to a saucepan and heat over medium-high. Whisk in the arrowroot slurry until well combined. Cook for several minutes or until sauce is reduced and thickened.