Using a sharp knife, slice the steak against the grain into thin strips. (If you are having a hard time slicing it thin, pop it in the freezer for 15 minutes, then slice it. This makes it easier to handle).
Place the sliced steak in a bowl or large ziplock bag with all of the "for the steak" ingredients (oil and spices). Toss to coat. Let marinate at room temp for 15-30 minutes.
Meanwhile, Place the sliced bell peppers and onions in a separate bowl, drizzle with 2 tbsp. avo oil and season, to taste, with salt and pepper. Set aside.
Heat a large skillet (preferably cast iron) over medium-high heat. When hot, add the steak and marinade and spread so that it in one layer (if possible) sear on the first side until golden brown, toss and continue to sear until all sides of the steak have a golden-brown crust (about 10 minutes total).
Using a slotted spoon or tongs, transfer steak to a bowl and cover with foil and let rest.
Meanwhile, place the onions and bell peppers into the same skillet (with all of the leftover juice from cooking the steak) and saute until tender, about 7 minutes. Be sure to scrape up all the yummy brown bits from the steak while you're sautéing these!
Divide lettuce amongst 4 bowls. Top with sliced avocado, steak, and sauteed onions and pepper. Drizzle with the creamy cilantro dressing. Serve with more fresh cilantro on top and a wedge of lime (optional).