Set a large nonstick skillet or a well-seasoned wok on the stove and place a paper towel-lined plate next to it.

Wrap the tofu in clean kitchen towels or paper towels and press it for 10 minutes to remove excess water. This helps it brown instead of steam.

While the tofu presses, drain the can of pineapple over a bowl. Reserve 1/2 cup of the juice and set the pineapple chunks aside.

Slice the scallions and keep them nearby for the finish.

In a medium bowl, whisk together the sweet chili sauce, the reserved pineapple juice, the soy sauce, and 1 tablespoon of the cornstarch until smooth.

Put the tofu cubes in a large bowl. Sprinkle the remaining 1 tablespoon cornstarch over the tofu and toss gently until the cubes have a light, even coating.

Add 2 tablespoons of the oil to the skillet and heat it over medium-high heat until the oil looks shiny.

Add the tofu to the hot skillet in a single layer. Cook for 3 to 4 minutes without moving it much, until the bottom sides are golden brown.

Turn the tofu pieces with tongs or a spatula. Cook for 4 to 5 minutes more, turning once or twice, until several sides are browned and the tofu feels firmer. Transfer the tofu to the plate.

Add the remaining 1 tablespoon oil to the same skillet. Add the red onion and cook over medium-high heat for 2 minutes, stirring often, until it starts to soften.

Add the red bell pepper and green bell pepper to the skillet. Cook for 3 to 4 minutes, stirring often, until the peppers are bright and just tender around the edges but still a little crisp.

Add the pineapple chunks to the skillet. Cook for 1 minute, stirring, just until the pineapple is hot and starting to take on a little color.