Remove and discard husks and silks from corn. Cut off corn kernels into a bowl; scrape milk and remaining pulp from cob with a paring knife to measure 3 cups. Set corn aside.
Heat yogurt-based spread in a large nonstick skillet over low heat; add onion. Cook over medium heat 3 minutes, stirring occasionally. Add corn and cook 4 minutes, stirring frequently. Add tomatoes; cook 3 minutes. Stir in parsley, salt, and pepper.