Local Mission Eatery is outstanding. They are making super fresh, innovative, and delicious food. And it's really close to the BART station at 24th and Mission, so it's quite easy to get there from Union Square. Universal Cafe is also in the Mission, but further from the BART and never disappoints. It would be a nice place to go on a sunny day for lunch - it will have all the quality of an evening meal, but with sunshine and cheaper prices. Universal Cafe changes up their menu really frequently - probably almost daily, depending on what is fresh.