Before starting, preheat the oven to 450˚F. Wash and dry all produce. Thinly slice tomato. Peel, then cut half the onion into 1/4-inch rounds (whole onion). Separate onion rounds into rings. Thinly slice half the jalapeño into 1/4-inch rounds, removing seeds for less heat. Core, then finely chop remaining jalapeño. (TIP: We suggest using gloves when prepping jalapeños!).

Add vinegar, jalapeño rounds, onions, 1 tsp (2 tsp) sugar and 2 tbsp (4 tbsp) water to a small pot. Season with salt.Bring to a simmer over medium-high heat. Cook, stirring often, until sugar dissolves, 1-2 min. Remove from heat. Transfer jalapeños and onions, including liquid, to a small bowl. Set aside in the fridge to cool.

Meanwhile, combine chopped jalapeños, cream cheese and half the cheddar cheese in another small bowl. (NOTE: This is your patty filling.)Combine spicy mayo and 1 tsp (2 tsp) water in another small bowl. (NOTE: This is your spicy mayo drizzle.)

Add beef, panko and 1/4 tsp (1/2 tsp) salt to a medium bowl. (TIP: If you prefer a firmer patty, add an egg to the mixture.) Season with pepper, then combine.Form beef into four 4-inch-wide burger patties (8 patties). Divide cheese filling between two patties (4 patties), then top with remaining patties. Firmly pinch edges of burgers together to seal in filling, then gently reshape into rounds.

Heat a large non-stick pan over medium-high heat. When hot, add 1/2 tbsp (1 tbsp) oil, then patties. (NOTE: Don't overcrowd the pan; cook patties in 2 batches if needed.)Sear, until golden-brown, 2-3 min per side.Remove from heat, then transfer patties to a parchment-lined baking sheet. Sprinkle remaining cheese over patties.Bake in the top of the oven until cooked through, 6-9 min.**

Meanwhile, add 1 tbsp (2 tbsp) reserved pickling liquid and 1 tbsp (2 tbsp) oil to a large bowl. Season with salt and pepper, then whisk to combine. Add spring mix, then toss to coat. Drain pickled jalapeños and onions, then discard remaining pickling liquid.Divide salad between plates. Top with tomatoes, patties, pickled onions and pickled jalapeños.Drizzle spicy mayo over top.