Pat the picanha dry with paper towels. Lightly score the fat cap in a crosshatch pattern, making shallow cuts about ½ inch apart. Season generously with salt, black pepper, and smoked paprika. Let the steak rest at room temperature for 30 minutes.
In a small saucepan over low heat, warm the oil and add the garlic. Cook for 1–2 minutes, just until fragrant and lightly golden.
Stir in the honey, soy sauce, Worcestershire sauce, citrus juice, and red pepper flakes. Cook briefly until smooth and glossy, then remove from heat. Divide the sauce in half and stir parsley into one portion for finishing.
Preheat the grill for two-zone cooking to 400–425°F (one direct heat zone and one indirect heat zone).
Place the steak fat-side down over direct heat. Grill for 4–5 minutes until the fat renders and becomes crisp and golden. Flip the steak.
Move the steak to indirect heat and close the lid. Grill until the internal temperature reaches 125–130°F for medium-rare, brushing with the reserved glaze every few minutes.
Remove from the grill, loosely tent with foil, and rest for 10 minutes.
Slice against the grain into thick slices and drizzle with the remaining clean garlic honey chili oil before serving.