Divide the grass fed beef into 8 equal portions for sliders, or 4 equal portions for larger burgers. Press a small well the middle of each burger to help the meat cook more evenly and not swell up in the middle during grilling. Season on both sides with the garlic salt and black pepper.

Preheat your grill to High (around 450-500 degrees F).

Slice each roll in half and spread the inside of each with about 1/2 Tablespoon of the garlic butter.

Rinse the tomatoes and place them in a vegetable grilling basket. Stir in the remaining Tablespoon of garlic butter.

Place both the burgers and tomatoes on the grill grates and cook for 6-8 minutes, flipping the burgers once and stirring the tomatoes frequently. During the last few minutes of cooking, top each burger with a slice of the mozzarella and place the buttered rolls on the grill grates to toast.