Preheat the grill to medium-high heat (450–500°F).
Pat the flank steak dry and season generously with kosher salt and black pepper.
Toss the corn, zucchini, and tomatoes with avocado oil, salt, and pepper.
Grill the steak for about 4–5 minutes per side for medium-rare.
Grill the vegetables for 2–3 minutes per side until lightly charred.
Remove everything from the grill and let the steak rest for at least 5 minutes.
Meanwhile, prepare the chimichurri by combining parsley, cilantro, garlic, oregano, red pepper flakes, vinegar, olive oil, salt, and pepper in a food processor. Pulse until combined.
Slice the steak against the grain into thin strips.
Chop the vegetables into bite-sized pieces and toss with fresh lemon juice.
Assemble the Grilled Chimichurri Steak Bowl by layering rice, greens, grilled vegetables, sliced steak, and generous spoonfuls of chimichurri sauce. Add cheese and herbs if desired.