Add steak marinade ingredients to a gallon-size Ziploc bag then squish to combine. Trim flank steak then add to the bag and marinate in the refrigerator for 1-6 hours.
For the Sweet Potatoes:
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.
If Using a Grill Pan:
Preheat an 11" or 12" cast iron grill pan over heat that’s between medium-high and high until it begins to smoke, 5-7 minutes.
Remove the steak from the marinade then pat it dry with paper towels. If your flank steak is too large to fit inside the grill pan, slice it in half and plan on grilling in two batches.
Add the steak into the pan then grill until browned char marks appear on the bottom, 4-6 minutes. Flip then grill for another 4-8 minutes or until the internal temperature of the thickest part of the steak reaches your desired temperature for doneness as read by a digital instant-read meat thermometer (see notes section below).
Remove the steak to a rimmed quarter sheet pan, or simply to a cutting board, then let it rest for at least 10 minutes. After resting, slice the steak against the grain (meaning, in the opposite direction of the long muscle fibers).
If Using a Gas or Charcoal Grill:
Preheat the grill over high heat with the lid down until the internal temperature reaches 475 - 500 degrees. Remove the steak from the marinade then pat it dry with paper towels.
Turn the heat down slightly then add the steak and grill according to the above directions, keeping the lid DOWN between flipping the steak.
Remove the steak to a rimmed quarter sheet pan, or simply to a cutting board, then let it rest for at least 10 minutes. After resting, slice the steak against the grain (meaning, in the opposite direction of the long muscle fibers).
For the Avocado-Cilantro Drizzle:
Add all ingredients 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.
To assemble:
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.