Whisk the reserved 3 tablespoons pineapple juice, vinegar, soy sauce, ketchup and sugar in a small bowl until smooth. Place tofu in a medium bowl; toss with 2 tablespoons of the sauce. Let marinate for 5 minutes. Add cornstarch to the remaining sauce and whisk until smooth.

Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Transfer the tofu to the skillet using a slotted spoon. Whisk any remaining marinade into the bowl of sauce. Cook the tofu, stirring every 1 to 2 minutes, until golden brown, 7 to 9 minutes total. Transfer the tofu to a plate.

Add the remaining 1 teaspoon oil to the skillet and heat over medium heat. Add garlic and ginger and cook, stirring constantly, until fragrant, about 30 seconds. Add bell pepper and cook, stirring often, until just tender, 2 to 3 minutes. Pour in the sauce and cook, stirring, until thickened, about 30 seconds. Add the tofu and pineapple chunks (or tidbits) and cook, stirring gently, until heated through, about 2 minutes more.

Tips for Two

Tofu

Storage: Rinse leftover tofu, place in a storage container and cover with water; it keeps up to 4 days in the refrigerator if the water is changed every day or 2; freeze tofu for up to 5 months. (Freezing tofu yields a pleasingly chewy result that some people prefer. Don't be surprised if the frozen tofu turns a light shade of caramel.)

Uses: Crumble and use instead of the meat in your favorite tuna or chicken salad recipe; dice and add to a vegetable stir-fry; add leftover silken tofu to smoothies.

MAKE AHEAD TIP: The tofu can marinate (Step 1) for up to 30 minutes.