1. Preheat the oven to 425 degrees Fahrenheit.
2. With a meat mallet or rolling pin, pound the flank steak to an even ⅓-inch thickness. This will give you more surface area to work with when stuffing it.
3. Season the steak with salt and pepper to taste on both sides, then lay it out flat in front of you. Sprinkle the chopped bacon over it in a single layer, then evenly layer on the spinach, tomatoes, and mushrooms, in that order. Roll the steak up lengthwise tightly into a log (roulade), then tie it with kitchen twine in 2 or 3 places to hold it together. (At this point, you can wrap the roulade in plastic wrap and refrigerate overnight, if you like. Bring to room temperature before cooking.)
4. Heat the oil in a 12 Inch Skillet over medium-high heat. When the pan is really hot, sear the roulade until browned on all sides, 2-3 minutes total.
5. Remove the pan from the heat and sprinkle the garlic all over the roulade. Place the skillet in the oven until the stuffing is hot but the meat is still pink in the center, 10-15 minutes.
6. Remove from the oven and let the roulade rest for 10 minutes. Remove the twine, slice into pinwheels, and serve!

Variations: Get creative with the filling. Try any combination of your favorite flavors, like sun-dried tomatoes, artichoke hearts, spinach, onions, mushrooms, bacon, sausage, uncured salami, green or black olives, fresh herbs, etc.