Preheat An Outdoor Grill For Medium-High Heat And Lightly Oil The Grate. Season The Ground Buffalo With Salt And Pepper; Form Into 8 Balls. Press A Cavity In Each Ball With Your Thumb Pressing Halfway Into Each Ball; Place A Tablespoon Of Blue Cheese Into The Hole And Seal The Meat Around The Cheese. Press Each Ball Into A Patty Shape. Cook The Burgers On The Preheated Grill Until Cooked To Your Desired Degree Of Doneness, 4 To 6 Minutes Per Side For Well Done. An Instant-Read Thermometer Inserted Into The Center Should Read 160 Degrees F (70 Degrees C). Spread The Toasted Buns With Mayonnaise. Place A Burger Patty Onto Each Bun Bottom, Then Place A Lettuce Leaf, Onion Rings, And Tomato Slice Onto Each Sandwich. Top With The Remaining Buns To Serve.