Soak the rosemary branches in cold water to cover.
Line a cookie sheet with a double layer of paper towels or a kitchen towel. Drain the tofu. Cut the block of tofu in half lengthwise, to create two thinner blocks of tofu, then cut the blocks each into thirds lengthwise and crosswise, giving you 18 cubes. Arrange the cubes in a single layer on the paper towels and place a double layer of paper towels on top. Press the cubes lightly to remove excess liquid. Set aside while you prepare the marinade.
Place the garlic cloves in the bowl of a food processor fitted with a metal blade. Cover and process for a few seconds to mince. Add the oregano leaves, lemon juice, olive oil, salt, and pepper. Cover and process for about 10 seconds to blend. Taste for seasonings. Transfer the drained tofu cubes to a clean plate. Spoon the marinade evenly over the tofu, using a rubber spatula to scrape the processor bowl. Set aside to marinate for a few minutes while you heat the grill, or cover and refrigerate overnight.
Heat the grill to medium. Remove the rosemary branches from the water. Carefully thread 4 tofu cubes onto each of two branches and 5 tofu cubes onto each of the remaining two branches. When the grill is heated, brush the grill rack with organic canola oil or organic sunflower oil. Arrange the kebabs in a single layer on the heated oiled rack and cook for about 3 minutes per side, until grill marks appear. Using tongs, carefully turn the kebabs to brown the other side. Transfer to a plate. Serve warm or chilled.