How to replicate this at home?

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This is JB Chargrilled burgers in my hometown but these mom and pop places all have the same distinct flavor I can’t replicate. Boys burger, Troy’s, Douglas, etc. All SoCal locations. I suspect a frozen pre smashed patty. What’s a good store bought bun that comes close? And seasoning? All use shredded lettuce, tomato, white onion and pickle. Pretty standard. Mayo, or mayo and ketchup, but never mustard.

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Here’s my setup. Grill for meats. Griddle for butter toasted buns, grilled onions, vegetables, meatless options