Preheat the oven to 375. Season pork loin roast with salt and pepper. Heat olive oil in a large cast iron skillet over medium-high heat. Sear the pork 2-3 minutes on all sides. Transfer pork to a baking sheet, roast for 15 minutes.
While the pork roasts, prepare the sweet and sour sauce. In a medium sauce pan on low heat add honey rice vinegar soy sauce and tomato paste. Cook, stirring often for 5 minutes. In a small bowl, whisk cornstarch and water to make a slurry. To the sweet and sour sauce, slowly add the slurry, stirring continuously until well incorporated. Reduce heat to low and simmer an additional 5 minutes.
After 15 minutes of the pork roasting, remove from the oven, baste with 1/2 the sweet and sour sauce. Add the onion and peppers to the baking sheet. Return to the oven for 15 minutes or until the internal temp of the pork loin roast reads 140. Broil on high for 5 minutes. Remove from the oven and rest pork for 10 minutes before slicing. Final temp of pork should be 145. Drizzle with remaining sweet and sour sauce. Serve over cooked white rice and garnish with scallions and sesame seeds.