Thoroughly wash and dry spinach and remove stems.
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. Serve immediately. If spinach releases too much water, you can drain mixture in a colander before serving. Taste and adjust seasonings again after draining.