In a medium mixing bowl, combine the finely chopped parsley, olive oil, red wine vinegar, minced garlic, red pepper flakes, salt, and pepper. Whisk everything together until well blended. Set aside to let the flavors marry.
Place the flank steak in a shallow dish or resealable plastic bag and pour half of the chimichurri sauce over it. Make sure the steak is well-coated, then cover and marinate in the fridge for at least 30 minutes (up to 2 hours for deeper flavor).
Heat your grill pan or outdoor grill over medium-high heat. Place the husked ears of corn directly on the grill and cook, turning occasionally, until the kernels are evenly charred and slightly blackened in spots, about 10 minutes. Remove from heat and let cool slightly, then cut the kernels off the cob.
Remove the steak from the marinade, letting the excess drip off. Grill the steak over medium-high heat for 4-5 minutes per side, depending on your preferred doneness. For medium-rare, aim for an internal temperature of about 130°F (54°C). Once cooked, transfer the steak to a cutting board and let it rest for 5 minutes before slicing thinly against the grain.
Divide the cooked quinoa between serving bowls. Top each bowl with sliced steak, charred corn kernels, sliced avocado, and halved cherry tomatoes. Drizzle the remaining chimichurri sauce over the top and garnish with lime wedges on the side for squeezing.
