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 4ppl) to a small pot. Season with salt. Bring to a simmer over medium-high heat. Cook, stirring often, until sugar has dissolved, 1-2 min. Remove pot from heat. Transfer onions, including liquid, to a medium bowl. Set aside in the fridge to cool.

While onions cool, core, then cut bell pepper into 1/4-inch slices. Roughly chop cilantro. Stir together sour cream and 1/4 tsp Chipotle powder in a small bowl. (NOTE: Reference Heat Guide.) Season with salt and pepper. Set aside.

Heat a large non-stick pan over medium-high heat. When hot, add 1 tbsp oil (dbl for 4ppl), then peppers. Cook, stirring occasionally, until tender-crisp, 3-4 min. Add beef, Mexican seasoning, 1/2 cup water (dbl for 4ppl) and 1/4 tsp Chipotle Powder. (NOTE: Reference Heat Guide.) Cook, breaking up beef with a spoon, 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 (from the medium bowl with onions) and 1 tbsp oil (dbl both for 4ppl) in a large bowl. Add spring mix and half the cilantro. Season with salt and pepper and toss to combine.

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