Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the cauliflower florets with 1 tsp olive oil, a pinch of sea salt, and black pepper.
Roast the cauliflower for 20-25 minutes until the edges are golden brown and tender.
While roasting, combine the parsley, cilantro, garlic clove, red wine vinegar, red pepper flakes, and 0.5 tbsp olive oil in a small blender or food processor.
Pulse the herb mixture until finely chopped but still textured, then set aside.
Season the skirt steak on both sides with garlic powder, sea salt, and black pepper.
Heat 0.5 tbsp olive oil in a cast-iron skillet over medium-high heat until shimmering.
Sear the steak for 3-4 minutes per side for medium-rare, then let it rest on a cutting board for 5 minutes.
Slice the steak thinly against the grain and serve topped with the zesty chimichurri alongside the roasted cauliflower.