Preheat and prep: Preheat the oven to 220°C (425°F). Position a rack in the middle so the vegetables roast evenly and get lightly caramelized. While the oven heats, pat the steak dry with paper towels — removing surface moisture is essential for a good sear (moisture creates steam and prevents browning). Season both sides of the steak generously with 1/2 tsp kosher salt, 1/2 tsp black pepper and a light dusting of smoked paprika; the paprika adds a smoky backbone that will pair with the roasted vegetables.

Toss and space the root vegetables: In a medium bowl, toss the carrot and parsnip sticks with 1 tbsp olive oil, 1/2 tsp kosher salt, 1/2 tsp black pepper, and the smashed garlic clove (if using). Spread them in a single layer on a rimmed baking sheet lined with parchment or a well-seasoned pan. Spacing is important — crowded vegetables steam rather than roast, so leave a little room between pieces for the edges to caramelize.

Roast the roots: Roast the vegetables for 20–25 minutes, turning once halfway through. Roast until edges are deeply golden and centers are tender when pierced with a knife. High heat encourages Maillard browning (caramelization), which concentrates the vegetables' sugars and builds savory complexity that contrasts the steak and chimichurri.

Bring steak to temperature: While the vegetables roast, let the seasoned steak rest at room temperature for 10–15 minutes (no more than 30). This evens the internal temperature so the steak cooks more predictably and helps avoid an overcooked exterior with a raw center.

Heat the grill or pan: Heat a heavy cast-iron skillet or outdoor grill to high — you want it smoking-hot. A very hot cooking surface creates a rapid sear that forms a caramelized crust, locking flavor into the meat. Brush or rub the steak lightly with the remaining 1 tbsp olive oil just before cooking to help conduct heat and prevent sticking.

Sear the steak: Sear the steak for about 3–4 minutes per side for medium-rare on a 2-cm thick flank/skirt cut (times vary with thickness). For precision, use an instant-read thermometer: remove at 52–55°C (125–131°F) for medium-rare — it will rise about 3–5°C while resting. Do not move the steak excessively while searing; steady contact forms an even crust.

Rest and finish: Transfer the steak to a cutting board and, if using, top with 1 tsp butter to add silkiness. Tent loosely with foil and rest 8–10 minutes. Resting allows muscle fibers to relax and juices to redistribute so the steak is juicy rather than losing its juices when cut.

Slice across the grain: Identify the direction of the meat fibers and cut the steak thinly across the grain into 3–4 mm slices. Cutting across the grain shortens muscle fibers and makes each bite tender — especially important for flank or skirt steak which is flavorful but a bit fibrous.

Build the salad: In a large bowl, lightly dress the mixed greens with 1 tbsp chimichurri (reserve 2 tbsp) and a quick splash (optional) of red wine vinegar or lemon if you prefer brightness. Toss just to coat — you want the greens lively, not saturated. Spoon the roasted root vegetables warm onto the greens; their heat helps wilt the leaves slightly and meld flavors.

Assemble and finish: Fan the thin steak slices over the dressed greens and roasted roots. Drizzle the reserved 2 tbsp chimichurri evenly over the steak and vegetables — the herb oil adds acidity and garlicky, herbal contrast. Finish with a light sprinkle of flaky sea salt and extra black pepper to taste. Serve immediately so the steak is warm and the roots still have a glowy roast.