Toss the cubed tofu with cornstarch in a large bowl until evenly coated, then transfer to a fine-mesh strainer and shake gently to remove any excess starch.

Heat the oil in a large nonstick skillet over medium-high heat until it shimmers. Add the tofu in a single layer and cook, turning occasionally, until crisp and deeply browned on all sides, about 10 to 15 minutes.

Transfer the browned tofu to a clean bowl and set aside, leaving the remaining oil in the skillet.

Add the bell peppers to the skillet and cook over medium-high heat until they are bright and crisp-tender, about 2 minutes.

Stir in the garlic, ginger, and curry paste. Cook until the paste is fragrant and beginning to darken slightly, about 1 minute.

Whisk in the coconut milk and sugar. Simmer gently until the sauce thickens enough to lightly coat the back of a spoon, about 5 minutes.

Remove from the heat and stir in the lime juice. Return the tofu to the skillet and toss gently to coat.

Serve immediately while the tofu is still hot and the sauce is bubbling.