Natures candy. They make everything taste better, and have a terrible habit of disappearing from the bowl in 1/10 of the time it took to make them. Proceed with caution, as you may go into withdrawal come Fall.
Arrange the tomatoes on a parchment-lined baking sheet cut-side up. Nestle the garlic cloves among the tomatoes. Drizzle with olive oil - enough so each tomato gets some - season with salt and pepper, and sprinkle the oregano leaves over the top.
Roast in the oven for 2 to 3 hours, until the tomatoes are shriveled but retain some moisture, and are sweet, sour, and unbelievably delicious.