Caprese Burgers

My husband is pretty traditional when it comes to hamburgers.  Usually I suggest different toppings, and he says he's okay with just ketchup and mustard.  I saw these caprese burgers on a few blogs, and thought they looked amazing, so I decided to put them on the menu and feed them to him anyways.  I could kind of tell he just wanted the same traditional toppings, but now he loves these burgers and has already asked for me to put them on the menu again.

Caprese Burgers
slightly adapted from Food Network
Ingeredients
Burgers
1.25 pounds ground sirloin beef
1/2 cup fresh or store-bought pesto, recipe follows
1/4 cup grated Mozzarella
1 1/2 teaspoons kosher salt
1/2 teaspoon freshly ground black pepper

Pesto Mayonnaise
1/2 cup mayonnaise
1/4 cup fresh or store-bought pesto

For Assembly: 
One ball fresh mozzarella, sliced into eight 1/4-inch-thick slices, patted dry with paper towels  
Extra-virgin olive oil for drizzling
4 hamburger buns, halved
2 medium tomatoes, sliced into rounds

Directions
1) For the burgers: Preheat a gas or charcoal grill.
2) Combine the beef, pesto, shredded mozzarella, salt and pepper in a large bowl.
3) Form the mixture into eight 4-inch-diameter patties, each about 3/4-inch thick. Grill for 5 minutes. Turn the burgers over and place a slice of mozzarella on top. Cook for about 5 minutes longer until the burgers are cooked through and the cheese is slightly melted. Allow the burgers to rest for 5 minutes.
4) For the pesto mayonnaise: In a small bowl, combine the mayonnaise and pesto until smooth. 
5) To assemble the burgers: Drizzle the cut side of the bread with olive oil and grill until lightly toasted, 1 to 2 minutes. Spread the pesto mayonnaise over the bottom halves of the grilled bread. Place the burgers on top and add 2 tomato slices. Add the top halves of the bread and serve.

 I thought these burgers were so easy to put together.  When we ate leftovers, we added avocadoes (which I know deviates from the true caprese form) which made them even more amazing.  I'm excited to make and eat more of these throughout the summer.