Mix tomatoes, garlic, and a teaspoon of olive oil in a small bowl. Set aside.
Lightly oil a 11x13-inch cookie sheet and then, using your fingers, spread the dough on the sheet, pressing it as far into the corners as possible. Spoon the tomato sauce evenly over the dough, leaving about a 1-inch border. Sprinkle the fresh basil and dried oregano over the sauce. Layer on, in the following order, sausage, onion slices, roasted red peppers if using, spinach, mozzarella, ricotta, parmesan, and red pepper flakes.
Very carefully (so as not to tear the dough), starting with a long side, roll the dough and filling into a long cylinder, making sure all the filling is enclosed. You might need two sets of hands to keep it under control. (If the dough does tear, just try to pinch the hole together and keep rolling.) Pinch the bottom and end seams to secure the filling, and place the stromboli seam side down on the cookie sheet. Brush the top with olive oil and sprinkle with sea salt.
Bake at for 45 minutes to an hour, or until the stromboli is golden brown, brushing again with oil during the last 5 minutes. Allow to cool, about 10 minutes.