Marinated sirloin with red peppers and artichokes

For the marinade/dressing:
6 tablespoons extra virgin olive oil
3 tablespoons red wine vinegar
1 tablespoon balsamic vinegar
1 teaspoon finely chopped fresh rosemary
1 teaspoon minced garlic
1/2 teaspoon kosher salt
Freshly ground black pepper
2 large artichokes
2 large red bell peppers
1 sirloin steak, about 2 pounds and 1-1/2 inches thick

1. To make the marinade/dressing: In a small bowl whisk together the marinade ingredients.
2. To prepare the artichokes: Trim the tops and tip of stems, remove the tough outside leaves, and halve the artichokes lengthwise. Steam the artichokes in a vegetable steamer over boiling water, covered, until tender, about 20 minutes. Transfer to a plate. When cool enough to handle scoop out the fuzzy choke and prickly center leaves and discard.
3. Cut the bell peppers in half lengthwise and remove the stems and seeds. Flatten the pepper halves with the palm of your hand.
4. Lightly brush the artichokes and bell peppers with about 1 tablespoon of the marinade.
5. Trim the steak of nearly all fat and place on a platter. Spoon 1 tablespoon of the marinade over each side of the steak, cover, and let stand at room temperature for about 20 minutes.
6. Grill the steak, peppers, and artichokes over Direct High heat, turning once halfway through grilling time. The steak will take 12 minutes for medium-rare, the peppers will take 10 to 12 minutes, and the artichokes will take 5 minutes. Remove from grill. Place the steak on a platter and cover lightly with aluminum foil. Allow grilled steak to stand for 5 minutes.
7. To serve: Cut the steak into thin slices, arrange on a heated platter, and surround with red peppers and artichokes. Spoon the remaining marinade/dressing over the meat and vegetables. Garnish platter with sprigs of fresh rosemary, if desired.