Preheat your oven to 425 F.
Lay the steak on a flat surface. Using a sharp knife held parallel to the cutting board, slice horizontally through the steak, stopping just short of the far side so you can open it up like a book.
1½ lb. flank steak
Flatten the steak to an even thickness using a rolling pin or meat hammer.
Heat some cooking fat in a skillet placed over medium heat, add the garlic, and cook for 1 minute.
2 garlic cloves, Cooking fat
Add all the spinach, season to taste, and cook for 2 minutes or until the spinach is wilted.
6 oz. spinach, Sea salt and freshly ground black pepper
Season the steak to taste.
In a bowl, combine the tomato, bell pepper, and spinach mixture.
1 bell pepper, 1 tomato
Press the filling all over the top of the steak.
Roll up the steak to enclose the filling. If any falls out the ends, tuck it back in.
Tie the steak into its rolled shape with some cotton twine.
Roast the steak for 30 to 35 minutes then finish it up by broiling for 5 minutes.
Let the meat rest for a few minutes.
Remove the twine, slice, and serve.