In a large pot or wok over medium heat, cook the onion in oil for 3 to 5 minutes, or until it begins to soften and become translucent.
Add the sliced carrots, minced garlic, and minced ginger to the pot.
Continue to cook and stir for another 3 minutes until fragrant.
While the vegetables cook, prepare the sauce.
In a medium bowl or jar, whisk together the pineapple juice, diced pineapple, brown sugar, rice vinegar, and tamari.
Add the arrowroot powder or cornstarch and stir vigorously until it is completely dissolved and no lumps remain.
Pour the sauce into the pot with the vegetables.
Add the diced bell peppers and tofu.
Stir constantly over medium heat until the sauce thickens, which should only take a minute or two.
Once thickened, reduce the heat to low, cover the pot, and let it simmer for 3 minutes to allow the flavors to meld and the vegetables to become tender-crisp.
Garnish with fresh parsley, if desired, and serve immediately over rice.