Lightly oil a grill rack and preheat grill.
Combine beef, 3/4 cup of the Gorgonzola cheese, all but 1 Tbsp of the sundried tomatoes, thyme, garlic, salt, and pepper in a large mixing bowl. Shape mixture into 6 patties about 3/4- inch thick. Place burger patties on grill rack, uncovered directly over medium heat.
Grill for 14 to 18 minutes or until thermometer inserted in centers registers 160 degrees, turning burgers once halfway through grilling. Remove burgers from grill. Top with remaining Gorgonzola and snipped dried tomatoes.
Serve on toasted sourdough rolls with sliced red onions and tomatoes.