Prepare the compote: Preheat the oven to 450 degrees F. Core the tomatoes and halve crosswise, then squeeze out the seeds. Put the tomatoes cut-side up on a baking sheet. Drizzle with 3 tablespoons olive oil; sprinkle with 1 teaspoon salt, and pepper to taste. Roast until shriveled, about 40 minutes. Cool slightly, then slip off the skins. Cut into chunks.
Toast the coriander and cumin seeds in a skillet over medium heat, about 2 minutes. Remove from the skillet and grind with a spice grinder or chop with a knife. Heat the remaining 2 tablespoons olive oil, the garlic and ginger in the skillet over medium heat and cook until beginning to brown, about 3 minutes. Add the tomatoes, ground coriander and cumin, and salt and pepper to taste.
Prepare the crabs: Heat 1/8 inch vegetable oil in a large nonstick skillet over medium-high heat. Put the polenta in a baking dish; add 2 teaspoons salt and 1 teaspoon pepper. Put the milk in a bowl. Dip the crabs in the milk and shake off the excess, then dredge in the polenta and shake off the excess.
Working in batches, fry the crabs, upside-down first, 3 to 4 minutes per side. Transfer to a paper towellined plate. Wipe out the skillet and add fresh oil between batches.
Reheat the compote and stir in the herbs. Serve the crabs with the compote and lime wedges.
Photograpg by Con Poulos
Recipe courtesy of Food Network Magazine