Marinate the steak: Combine skirt steak, balsamic vinegar, olive oil, garlic, salt, and pepper. Refrigerate for 1 hour. Let sit at room temperature for 20 minutes before grilling.
Grill the peppers: Grill red bell and Fresno peppers for 6–8 minutes, turning until charred. Lower heat, cover, and cook bell peppers 12 more minutes until soft.
Make the relish: Peel skins, remove stems, and finely chop. Combine with vinegar, olive oil, honey, parsley, oregano, salt, and pepper.
Prepare zucchini salad: Toss shaved zucchini with olive oil, lemon zest, lemon juice, parsley. Let sit 10 minutes. Season and top with parmesan before serving.
Grill the steak: Heat grill to medium-high. Grill steak 3 minutes on one side, flip and cook 3–4 minutes more. Let rest 5 minutes.
Serve: Slice steak against the grain. Plate with relish on top and salad on the side. Sprinkle with flaky sea salt if using.
