Step 1

Prepare marinade in a small bowl by whisking together balsamic vinegar, olive oil, lemon juice, mustard, and salt.

Step 2

Remove stems from mushroom caps and wipe clean with a damp paper towel. Place mushrooms in a large resealable plastic bag. Pour in marinade, seal bag, and toss to coat thoroughly. Let marinate for at least 30 minutes, turning halfway through for even coverage.

Step 3

Coat fryer with some oil to prevent sticking. Add portobellos to air fryer basket and cook at 370 degrees for 7 minutes.

Step 4

Meanwhile... prepare your toppings of choice. Combine pesto and mayo, sauté some spinach, slice some tomatoes and red onions.

Step 5

Once cook time is complete, remove mushrooms and allow to rest on separate plate for a few minutes. (They will give off quite a bit of liquid, so don't place it on a bun too quickly or your buns will go soggy.)