Preheat a greased barbecue grill to medium heat.

In a large bowl, combine the lean ground beef, fajita seasoning mix, and fresh ground black pepper.

Mix the ingredients thoroughly.

Divide the beef mixture into 8 equal portions.

Shape each portion into a patty about 3/4 inch thick.

Place 4 patties on a clean surface.

Top each of the 4 patties with a slice of monterey jack pepper cheese, tearing cheese slices as needed to fit the patties.

Cover each cheese-topped patty with one of the remaining patties.

Press the edges of the patties together to seal in the cheese.

Place the sealed hamburgers on the preheated grill.

Close the grill lid and grill the burgers, turning once, for 8-10 minutes per side.

Ensure the internal temperature reaches 160 degrees Fahrenheit using an instant-read thermometer inserted into the center of the burger.

Remove the burgers from the grill and let them rest for a few minutes.

Serve the burgers in whole-grain buns.

Add desired toppings such as lettuce, tomato slices, red onion slices, avocado slices, and salsa.