(I usually use the packaged, pre-washed spinach so that I don't get too much water in this dish. Otherwise, be sure to dry the leaves very, very well.) Using half the ingredients and working in batches, heat olive oil in a large skillet over moderate heat.
Saute garlic about one minute.
Add spinach leaves, increase heat to high, and stir until evenly wilted, about 2 minutes.
Add salt, pepper, and tomatoes.
Cook an additional minute.
Stir in grated Parmesan, remove from heat, taste, and adjust seasonings.
If spinach releases too much water, you can drain mixture in a colander before serving.