Spread the mayonnaise on one half of two slices of bread. Place on the cast iron skillet on medium heat.
Spread the mozzarella cheese evenly on the slice of bread. Spread the tomato slices evenly on top of the cheese.
Spread pesto on one half of the additional slices of bread. Place on top of the tomatoes.
Spread mayonnaise on top of the top slice of bread.
Once the cheese on the bottom is melted (about 3-4 minutes) flip the grilled cheese. Cook another 3-4 minutes. Remove from the heat and serve immediately.
Notes
-save leftovers in the refrigerator wrapped in tin foil for up to 5 days.-these ingredients do not stand up well to freezing.