Combine soy sauce, canola oil, lime juice, cumin, chili powder, garlic, salt and pepper and crushed red pepper flakes in a medium bowl and whisk to combine.
Place steak in a large ziplock bag and pour the marinade on top. Seal bag, squeezing out as much air as possible.
Lay flat in the refrigerator and marinate for at least 2 hours, turning every couple of hours, or overnight.
Make the dressing by combining all ingredients in a blender or food processor and blending until smooth.
Refrigerate for at least 10 minutes before serving. (Dressing can be made several days in advance).
Remove steak from marinade and discard marinade.
Allow steak to rest while you heat your over medium heat. Lightly oil the grill and cook the steak for 3-4 minutes on each side, flipping only once, until medium rare.
Remove to a plate and allow to rest while you prepare the salad.
Add 1 tablespoon olive oil to a large skillet or grill pan over high heat.
Add the chopped bell peppers and onions. Season with salt and pepper and cook for 2-3 minutes, tossing, until slightly charred.
Place the chopped lettuce in a large bowl.
Place sliced avocado and grilled peppers and onions on top.
Slice the flank steak into very thin slices and place on top of the salad.
Drizzle with cilantro lime dressing. Serve immediately.