Place steak in shallow dish. Whisk together next 5 ingredients (through garlic). Pour marinade over steak, and coat both sides. Cover; refrigerate 1 hour.
Prepare medium-high grill, or set grill pan over medium-high heat. Coat corn with cooking spray; grill about 5 minutes or until well-marked on all sides. Remove from grill, and let cool. Cut kernels from ears with a sharp knife; set aside.
Remove steak from marinade, season both sides with salt. Grill 2–3 minutes per side or until internal temperature reaches 145° (for medium rare). Transfer to cutting board; let rest 5 minutes before slicing.
Toss jícama with lime juice. Put spinach in a large bowl. Add roasted peppers, reserved corn, jícama, avocado, and queso fresco. Toss with bottled Southwestern-style dressing (or our Roasted Poblano Dressing; get the recipe at Health.com/poblano).
Thinly slice steak against the grain. Divide salad among 4 plates, arranging steak on top. Sprinkle with cilantro; serve.