Remove the Impossible patty from the refrigerator (if chilled) or take it from the freezer and let sit 5 minutes while you assemble toppings. Preheat a heavy skillet or cast-iron pan over medium-high heat for 2–3 minutes until hot.

Season patty

Pat the patty dry with a paper towel if there is excess moisture. Lightly brush or rub both sides with the vegetable oil. Sprinkle approximately 1/2 tsp kosher salt and 1/2 tsp freshly ground black pepper evenly over both sides.

Cook patty

Add a small drizzle (about 1 tsp) of oil to the hot skillet and swirl to coat. Place the patty in the pan and cook without moving for 2–3 minutes to develop a sear. Flip and cook another 2 minutes. Press gently with a spatula once after flipping to increase contact for an even sear. If using a frozen patty, cook 3–4 minutes per side. Total cooking time should be about 4–6 minutes for fresh patties, 6–8 minutes for frozen.

Melt cheese

During the final 30–60 seconds of cooking, place the cheddar slice on the patty. Cover the pan with a lid or tent with foil for 30–45 seconds to help the cheese melt and the patty finish cooking. Remove from heat once cheese is melted and internal temperature reaches around 160°F (71°C) or until desired doneness and warmth.

Toast bun

While the patty rests 1 minute, heat another small pan or wipe the same skillet clean and add 1 tsp butter. Split the bun and place cut sides down in the buttered pan over medium heat. Toast for 30–60 seconds until golden and lightly crisp. Remove and set on a plate.

Toppings & Assembly

Prepare condiments

In a small bowl, mix 1 tablespoon mayonnaise with 1 teaspoon ketchup and 1 teaspoon yellow mustard. Taste and adjust if you prefer more ketchup or mayo.

Assemble burger

Spread half of the mayo-ketchup-mustard mix on the bottom bun. Place the lettuce leaf on the bottom bun, then add the cooked Impossible patty with melted cheese. Top the patty with tomato slices, red onion rings, and pickle slices. Spread the remaining sauce on the top bun and place it over the toppings.

Finish and serve

Press gently to compress slightly, cut in half if desired, and serve immediately. Provide extra ketchup or pickles on the side if preferred.