Add steak marinade ingredients to a gallon Ziplock bag then squish to combine. Slice flank steak in half if too large to fit inside an 11" or 12" cast iron skillet, then add to marinade and refrigerate for 1-6 hours.
Heat oven to 425 degrees then line a half sheet pan with parchment paper or spray with nonstick spray. Add sweet potatoes then drizzle with extra virgin olive oil and season with garlic powder, salt, and pepper. Toss with your fingertips to coat then spread potatoes into an even layer and roast for 25-30 minutes, or until golden brown and tender, stirring with a spatula halfway through.
Place a large cast iron skillet over heat that's just a touch below high. Add enough high heat cooking oil to create a very thin layer on the bottom of the skillet then, when it begins to smoke, add the steak. Be careful as the oil might spit a bit, and turn the fan up, too! Let steak sear for 2-4 minutes on each side for medium-rare, then transfer to a cutting board and repeat with second piece of steak. If you prefer your steak medium or medium-well, add both pieces of steak back into the skillet off the heat then let the residual heat of the skillet continue to cook the steak for severalminutes. Let steak sit for a minimum of 10 minutes on the cutting board before slicing into thin strips against the grain.
Add all ingredients for the Avocado-Cilantro Drizzle except water to a small food processor or blender then pulse until roughly chopped. Add 2 Tablespoons water then process until smooth, adding up to 2 more Tablespoons water to get the sauce to a smooth but not runny consistency. Taste then add more salt and pepper, or lime juice if necessary.
Scoop rice into bowls then top with sliced steak, roasted sweet potatoes, sliced avocado, and baby arugula or baby spinach. Top with Avocado-Cilantro Drizzle then serve.