Heat large covered saucepot of water to boiling over medium-high heat. Add corn and cook 4 to 5 minutes or until corn is tender; drain. When cool enough to handle, cut corn from cobs.
In large bowl, whisk together garlic, oil, vinegar, mustard, salt and cayenne. Add cheese, tomatoes, oregano and corn, and toss to combine. Let stand at least 10 minutes before serving. If not serving right away, cover and refrigerate up to 1 day in advance. Serve garnished with spinach leaves, if desired. Makes about 4½ cups.