Toasted Burger Buns: I think the taste and the texture of buns are best when lightly toasted. To toast a bun on a grill, grill pan, or griddle, split the bun open, place it cut-side down on the grill, and grill until light golden brown, about 10 seconds. Alternatively, you can place the split bun halves cut-side up on a baking sheet and cook them under a preheated broiler until light golden brown, about 30 seconds. Keep a close eye on them and don't let them get too brown or else that texture will take on a life of its own and defeat the purpose of starting with a soft bun. IF USING A GRILL: Heat a gas grill to high or heat coals in a charcoal grill until they glow bright orange and ash over. Brush the burgers with the oil. Grill the burgers until golden brown and slightly charred on the first side, about 3 minutes for beef and 5 minutes for turkey. Flip over the burgers. Cook beef burgers until golden brown and slightly charred on the second side, 4 minutes for medium rare (3 minutes if topping with cheese; see step 3) or until cooked to desired degree of doneness. Cook turkey burgers until cooked throughout, about 5 minutes on the second side. IF USING A GRILL PAN: Heat a grill pan over high heat on top of the stove. Cook the burgers as for a grill, above. IF USING A SAUTE PAN OR GRIDDLE (PREFERABLY CAST IRON): Heat the oil in the pan or griddle over high heat until the oil begins to shimmer. Cook the burgers until golden brown and slightly charred on the first side, about 3 minutes for beef and 5 minutes for turkey. Flip over the burgers. Cook beef burgers until golden brown and slightly charred on the second side, 4 minutes for medium rare (3 minutes if topping with cheese) or until cooked to desired degree of doneness. Cook turkey burgers until cooked throughout, about 5 minutes on the second side.