Heat olive oil in a small sauce pan over medium-low heat. Add the garlic and sautée for 1 minute. Add the tomatoes, basil, sea salt, and sugar and stir to combine. Cover the pot with a lid, leaving only a small crack for steam to escape, and simmer over low heat for 15-20 minutes, or until the sauce has thickened. Stir the chopped Swiss chard into the sauce and continue cooking it for about two minutes, until the Swiss chard has wilted. Place the lid on the sauce pan and remove it from the heat.