Heirloom Tomatoes Stuffed with Corn and Zucchini Succotash

8 	slightly firm medium heirloom tomatoes
3 	tablespoons vegetable oil, divided 
2 	cups white corn kernels (cut from 3 to 4 ears)
2 	cups chopped onions
2 	garlic cloves, peeled
1 	cup chopped tomatoes
3 	cups ¼ inch cubes zucchini (from about 12 ounces)
2 	tablespoons chopped fresh epazote or cilantro
1 	teaspoon dried oregano (preferably Mexican oregano)

Core whole tomatoes, creating 2½-inch opening at top. Using melon bailer, scoop out tomato, transferring juices and pulp to small bowl (for filling). Turn tomatoes, cut side down, onto paper towels to drain. Heat 1 tablespoon oil in large deep skillet over medium-high heat 1 to 2 minutes. Add corn and toss until tender and beginning to color, 2 to 3 minutes. Using slotted spoon, transfer corn to medium bowl. Add remaining 2 tablespoons oil to same skillet. Add onions and saute until translucent, about 4 minutes. Using garlic press, squeeze in garlic; stir 30 seconds. Add chopped tomatoes and reserved tomato pulp and juices. Saute until tomatoes are soft, about 5 minutes. Mix in zucchini, epazote, oregano, and corn. Saute until sauce thickens and zucchini is just tender, about 8 minutes. Season generously with salt and pepper. Arrange tomato shells, cut side up, on small baking sheet. Spoon in filling, mounding high. DO AHEAD Can be made 2 hours ahead. Let filled tomatoes stand at room temperature. Preheat oven to 350°F. Bake tomatoes until filling is heated through and tomato shells are just tender, about 25 minutes.

MAKES 8