In a bowl, add the pork cubes, the baking soda, 2 cloves of the minced garlic, the ginger, and the soy sauce and mix well to combine.
Allow the pork to marinate until it is infused with flavor and the meat is tenderized, about 10-15 minutes.
In a separate bowl, add the rice vinegar, the brown sugar, the chicken broth, the ketchup, the tomato paste, the pineapple juice, 1/2 teaspoon of the cornstarch, and 1 teaspoon of the salt and whisk to combine. Set the sauce mixture aside.
Discard the marinade, then season the pork with the extra salt and the black pepper.
Add the remaining cornstarch to the pork mixture and toss to coat.
In a skillet over medium-high heat, add 1 cup of the oil.
Add the pork cubes to the hot oil and fry them, turning them occasionally, until they are lightly golden but not quite cooked through, about 2-3 minutes.
Using a slotted spoon, transfer the pork to a plate.
Add 1 cup of the reamaining oil to the skillet and heat it until shimmering.
Add the pork cubes to the hot oil and fry again until they are golden-brown, crispy, and reach an internal temperature of 145 degrees F, about 2-3 minutes.
Using a slotted spoon, transfer the double-fried pork to a plate.
In a large wok or pan over medium-high heat, add the remaining oil.
Add the green bell peppers, the red bell peppers, and the onions to the hot oil and cook, while stirring, for 1 minute.
Add the remaining minced garlic to the vegetable mixture and cook, while stirring, until fragrant, about 30 seconds.
Add the sauce mixture to the vegetable mixture and cook, while stirring, until the sauce becomes thick and glossy, about 2 minutes.
Add the double-fried pork and the pineapple chunks to the wok and toss well to coat.
Cook, while stirring, until everything is heated through, about 2 minutes.
Plate the pork mixture over the rice.
Top with the scallions and serve.