Preheat a 6-quart air fryer to 350˚ F. Toss the plantains with the vegetable oil and 3/4 teaspoon kosher salt. Add to the air fryer basket in an even layer and cook until tender, 3 to 4 minutes per side.
Transfer the plaintains to a large piece of parchment and cover with another piece of parchment; smash each plantain with the bottom of a glass. Increase the fryer temperature to 400˚ F. Return the plantains to the fryer in an even layer (it’s OK if they overlap slightly) and continue cooking until crisp, about 4 more minutes per side. Sprinkle with sea salt. Serve with salsa verde.