Press the tofu. Wrap the block of tofu in a clean kitchen towel and set something heavy on top (like a skillet) for 15–20 minutes. This step helps the tofu crisp up.

Preheat the air fryer to 390°F (200°C). A hot basket helps the tofu get golden fast.

Cube and season. Cut the tofu into 1-inch cubes. In a bowl, toss gently with 1 tablespoon oil, garlic powder, onion powder, salt, and pepper. Sprinkle 2 tablespoons cornstarch over the tofu and toss again until evenly coated.

Air fry the tofu. Arrange the cubes in a single layer in the basket. Cook for 12–15 minutes, shaking halfway. They should be crisp and lightly browned at the edges.

Sauté the veggies. While the tofu cooks, heat a large skillet over medium-high. Add a small splash of oil, then the bell peppers and red onion. Stir-fry for 3–4 minutes until slightly tender but still crisp. Add pineapple and cook 1 minute more. Remove to a plate.

Make the sauce. In the same skillet, add ketchup, vinegar, pineapple juice, brown sugar, soy sauce, sesame oil, garlic, and ginger. Bring to a gentle simmer. Stir the 1 teaspoon cornstarch with 2 teaspoons water to make a slurry, then whisk it into the sauce. Simmer 1–2 minutes until glossy and slightly thickened.

Combine everything. Add the crispy tofu and sautéed veggies to the skillet. Toss to coat in the sauce. Cook 1 minute to warm through.

Taste and adjust. Add a splash more vinegar for tang, a pinch more sugar for sweetness, or a dash of soy sauce for depth. If the sauce seems too thick, loosen with a tablespoon of water or pineapple juice.

Serve. Spoon over rice or noodles. Garnish with green onions and sesame seeds. A squeeze of lime is great if you like extra brightness.