Combine the ground meat, salt, pepper, garlic, thyme, and red pepper flakes and mix, just until combined. Then, gently form 4 patties.
Grill the patties over medium heat until the internal temperature reaches 160 degrees F, about 5 minutes per side. Then, add one slice of cheese to each patty and grill for one minute more.
Serve the patties on the toasted rolls, topped with warmed marinara sauce.