Preheat the oven to 350 F. Wash and rub the sweet potatoes under warm running water to remove debris and dirt, pat them dry with paper towels, then slice each lengthwise in half.

Line a large baking sheet with parchment paper. Rub the cut sides of sweet potatoes with olive oil and season generously with salt and freshly ground black pepper. Place the sweet potatoes (cut sides down) on the baking sheet.

Bake for about 30 minutes (or longer), until the potatoes are soft when you poke them with the fork.

Remove the roasted sweet potatoes from the oven and let them cool slightly. Remove the skins, and mash the soft flesh with 2 tablespoons of butter in a large bowl. Set aside.

While you roast the sweet potatoes, prepare the spinach sauce.

In a food processor, combine spinach, garlic, olive oil, balsamic vinegar, cumin, chili powder, and salt. Close with the lid.

Process/blend for about 3 or 5 minutes until the mixture is smooth.

Turn off the food processor and remove the sharp centerpiece. Using a flexible spatula, pour the sauce from the food processor into a medium-deep bowl. Set aside.

Season the flank steak on both sides with chili powder, salt, and freshly ground black pepper, using 1 tablespoon of olive oil to rub the spices in. Add more seasoning to taste.

Heat an empty large (at least 12-inch) cast-iron skillet over medium heat for 3 minutes. Add 1 tablespoon of olive oil. Add the whole flank steak and cook on one side on medium heat for a total of 5 minutes.

Flip the flank steak over to the other side, reduce heat to low-medium, and cook for about 5 minutes or more until the steak is cooked to your liking.

Remove the steak from the skillet and put it on a plate. Slice the steak against the grain into thin strips about 1-inch wide.

To the same, now empty, cast-iron skillet, add 1 more tablespoon of olive oil. Add cooked and sliced flank steak, and reheat it coating it thoroughly with the olive oil sauce (and all the juices and spices in the pan) on medium heat for a minute or two.

Season with salt and pepper, if needed. Remove from heat.

Divide pan-seared flank steak and mashed sweet potatoes among 4 serving plates. Drizzle the steak with the spinach sauce in some spots.

Top hot mashed potatoes with butter and coarsely ground black pepper.

Top with chopped fresh cilantro or parsley.