Preheat your air fryer to 400°F (200°C).
Wash the bell peppers and carefully cut off the tops. Remove the seeds and membranes.
Heat the olive oil in a medium skillet over medium heat.
Add the lentils, cooked rice, Italian seasoning, red pepper flakes (if using), tomato sauce, corn, chopped tomatoes, and zucchini. Stir well to combine.
Cover and cook for 8–10 minutes, stirring occasionally, until the zucchini is tender and the filling is heated through.
Stir in the shredded cheese and chopped spinach. Cook for another 2–3 minutes until the cheese melts and the spinach wilts.
Spoon the filling into each bell pepper until full. Sprinkle extra cheese over the tops.
Arrange the stuffed peppers upright in the air fryer basket.
Air fry the Vegetarian Air Fryer Stuffed Peppers for 10–15 minutes, or until the peppers are tender and the cheese is melted and lightly golden.
Serve immediately with sour cream, salsa, and a fresh side salad if desired.