Lay flank steak flat on a cutting board and butterfly if needed for even thickness.
Cover with plastic wrap and pound lightly with a meat mallet.
Brush steak with olive oil and season with salt, pepper, and garlic powder.
Spread spinach, cheese, roasted peppers, and herbs evenly over steak.
Starting from one long side, tightly roll steak into a log.
Secure with kitchen twine every 1–2 inches.
Slice between twine to create pinwheel rounds.
Preheat grill to medium-high heat.
Grill pinwheels for 4–5 minutes per side until desired doneness is reached.
Let rest for 5 minutes before serving.