Blue cheese variation: Substitute 1/2 cup chopped roasted red peppers or 1/2 cup chopped artichoke hearts for the sun-dried tomatoes (skip Step 2). Mash 1/2 cup blue cheese with 2 tablespoons milk until smooth and substitute for the Boursin in Step 4.Meat-Buying Tips:Make sure that packaged meat isn't past its "sell-by" date and that there's not much moisture in the packaging.Touch it if possible—it should be firm and not soft.Look for bright red (not gray) meat. Vacuum-packed meat will be darker looking and should turn red as soon as it's exposed to air.To oil a grill rack: Oil a folded paper towel, hold it with tongs and rub it over the rack. (Do not use cooking spray on a hot grill.)
Place sun-dried tomatoes in a bowl; pour boiling water over them and let steep until softened, about 10 minutes. Drain and chop.
Meanwhile, place steak between 2 large pieces of plastic wrap. Pound each side of the steak thoroughly with the pointed side of a meat mallet until the steak is an even 1/4-inch thickness.
Rub garlic all over one side of the steak. Spread cheese lengthwise in a 3-inch-wide strip down the middle of the steak. Top with the sun-dried tomatoes and spinach. Starting at one edge of a long side, roll the steak up tightly, tucking in the filling as you go.
Carefully rub salt and pepper all over the outside of the steak roll. Turn the roll so the overlapping edge is on top. Push 8 skewers, evenly spaced, through the roll, close to the overlapping edge to hold the roll together. Slice the roll into 8 equal portions, roughly 1 to 1 1/2 inches thick, with a skewer in each. Lay the slices on their sides and push the skewer through so it sticks out about 1 inch.
Oil the grill rack (see Tip). Grill the pinwheels 3 to 4 minutes per side for medium-rare. Use a spatula when turning them to prevent too much filling from falling out. (Don't worry if the ends of the skewers burn. They will still hold the pinwheels together.) Remove the skewers; let the pinwheels rest for 5 minutes before serving.