Season pork with salt & pepper and toss with 1 tablespoon cornstarch. Refrigerate for 15 minutes (while you prepare the remaining ingredients).
To make the sauce in a small bowl, whisk together water, pineapple juice, soy sauce, brown sugar, sriracha, and sesame oil.
Heat 1 tablespoon of oil over medium-high heat in a large pan. Stir fry pork in small batches until browned (it does not need to be cooked all the way through). Remove from pan and set aside.
Add remaining oil to the pan if needed and add vegetables. Stir-fry until tender-crisp, about 3 to 4 minutes. Add garlic and ginger and cook for 30 seconds or until fragrant. Remove the vegetables from the pan.
Add the stir fry sauce and bring to a simmer.
Combine 1 tablespoon cornstarch with 2 tablespoons water and whisk into the boiling sauce a little bit at a time to reach the desired consistency.
Add pork, pineapple and vegetables back to the pan and let simmer 2 minutes or just until heated through.
Serve with rice or noodles.