Using a sharp knife, cut a slit along the length of the plantain skin to make peeling easier; peel the plantain and cut it into eight 1-inch pieces.

In a small bowl, stir together 1 cup water, 1 teaspoon kosher salt, and 3/4 teaspoon garlic powder until the salt is dissolved.

Preheat the air fryer to 400°F.

Lightly spray the plantain pieces with olive oil spray and place them in a single layer in the air fryer basket (work in 1–2 batches as needed to avoid overcrowding). Air fry 6 minutes at 400°F.

Remove the plantain pieces while hot and flatten each piece with a tostonera, the bottom of a jar, or a measuring cup until flattened (they will spread out).

Briefly dip each flattened piece into the seasoned water, shake off excess, and set them aside on a plate.

If needed, re-preheat the air fryer to 400°F. Arrange the flattened plantains in a single layer in the basket (again working in batches if necessary). Lightly spray the top side with olive oil.

Air fry 5 minutes, flip each piece, spray the other side with olive oil, then air fry another 5 minutes, or until the tostones are golden and crisp.

Remove the tostones, give them a final light spray of olive oil if desired, and serve immediately.