Preheat oven to 450°F.
Prepare a baking sheet pan by lining with non-stick parchment paper. Add all the chopped veggies to the pan.
In a small bowl, add olive oil (just 2 tablespoons), tahini, cumin, paprika, onion powder, salt, black pepper, garlic, lemon juice, and parsley. Whisk all together with a fork.
Pour the marinade over the veggies and coat evenly using your hands to massage it in. Pop in the oven for 40 minutes, making sure to flip halfway through so they evenly roast.
In the meantime, we'll cook the steak. In a food processor, add the garlic cloves, oregano, cilantro, mint, paprika, salt, lemon black pepper, and 1 tablespoon of olive oil. Blend until you have a puree.
Coat the flank steak on every side with the puree. Set aside.
Heat a skillet or pan over medium-high heat for 5 to 10 minutes, just until very hot. Add one tablespoon of olive oil to coat the pan.
Drop the steak in on one side and allow to sear for about 6 to 7 minutes. After the first side is done, add the butter to the pan and flip the steak over. Tilt the pan to the side, and spoon the butter over the top of the steak - basting it. Give the other side another 6 to 7 minutes for medium rare to medium.
Take off the heat and allow to rest for 5 minutes.
Cut against the grain and once the veggies are done cooking, serve with!