Before starting, wash and dry all produce. Heat Guide for Steps 2 and 3 (dbl for 4 ppl): 1/8 tsp mild, 1/4 tsp medium and 1/2 tsp for spicy! Add onions, vinegar, 2 tbsp water and 2 tsp sugar (dbl both for 4 ppl) 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 the pot from heat. Transfer onions, including pickling liquid, to a medium bowl. Place in the fridge to cool.

Meanwhile, core, then cut pepper into 1/4-inch slices. Roughly chop cilantro. Add sour cream and 1/4 tsp chipotle powder to a small bowl. (NOTE: Reference heat guide.) Season with salt and pepper, then stir to combine. Set aside.

Heat a large non-stick pan over medium-high heat. When hot, add 1 tbsp oil (dbl for 4 ppl), then peppers. Cook, stirring occasionally, until tender-crisp, 3-4 min. Add beef, Mexican Seasoning, 1/2 cup water (dbl for 4 ppl) and 1/4 tsp chipotle powder. (NOTE: Reference heat guide.) Cook, breaking up beef into smaller shreds, until fragrant and heated through, 4-5 min.**

Wrap tortillas in paper towels. Microwave until tortillas are warm and flexible, 1 min. (NOTE: You can skip this step if you don't want to warm the tortillas!)

Whisk together 1 tbsp pickling liquid and 1 tbsp oil (dbl both for 4 ppl) in a large bowl. Add spring mix and half the cilantro. Season with salt and pepper, then toss to combine.

Drain pickled onions, discarding remaining pickling liquid. Divide tortillas between plates. Top with beef filling and pickled onions. Spoon chipotle sour cream over top and sprinkle with remaining cilantro. Serve salad on the side.