Preheat the oven to 475°F (245°C). Line a rimmed baking sheet with parchment paper or lightly oil it.
In a large bowl or directly on the sheet pan, toss the sliced beef with black pepper and the tablespoon of flour until evenly coated.
Add 1 tablespoon of oil and the patted-dry pickled ginger to the beef, tossing to combine; spread the beef to one side of the prepared sheet pan.
Place the broccoli florets on the other side of the sheet pan; drizzle with remaining oil, season with salt and pepper, and toss to coat.
Bake at 475°F for 10 minutes until the broccoli begins to roast and the beef is mostly cooked through.
While the pan roasts, whisk together the sauce: tamari (or soy), maple syrup (or honey), gochujang, ginger juice, chopped garlic, and 1 tablespoon toasted sesame oil; stir in the sesame seeds.
Remove the sheet pan from the oven and lift the broccoli off the pan onto a plate to keep it from overcooking.
Pour about two-thirds of the sauce over the beef on the sheet pan and toss the beef in the sauce to coat evenly.
Switch the oven to broil and broil the beef 2–5 minutes, watching closely, until edges begin to crisp and sauce caramelizes.
Meanwhile, in a bowl toss the sliced Persian cucumbers with chopped green onions, chili flakes, a pinch of salt, and 1–2 teaspoons toasted sesame oil.
Serve the broiled beef with the roasted broccoli and cucumber salad. Offer the remaining sauce and a drizzle of spicy mayo on the side or over steamed rice if desired.