Place the feta cubes on a paper towel and pat off any excess liquid.
Add the flour to a small, shallow bowl. In another bowl, whisk together the egg and milk until fully combined. Add the breadcrumbs to a third bowl.
Dip a feta square in the flour, followed by the egg mixture, and then the breadcrumbs. Dip the feta back into the egg and then back into the breadcrumbs a second time.
Transfer the feta square on a small plate or baking tray and repeat with the remaining croutons.
Place the feta squares in the freezer to chill for 20-30 minutes.
Once the feta croutons are cold to the touch, transfer them to an air fryer basket and cook at 400°F until they are golden brown on the edges, about 7-10 minutes. Set aside until ready to serve.
Make Dressing & Assemble the Salad
In a small bowl, whisk together the red wine vinegar, lemon juice, dijon mustard, and Italian seasoning. Slowly stream in the olive oil, whisking constantly until incorporated.
Combine the lettuce, tomatoes, red onion, and cucumber in a large serving bowl. Drizzle over the vinaigrette and toss to combine. Top with the feta croutons and serve immediately.
Notes
Storage: The feta croutons can be stored in an airtight container. They will last about 3-4 days in the fridge. They can be eaten cold or reheated in the air fryer at 360F for 2 to 3 minutes.