Heat broiler. Drizzle 1 tablespoon oil on a rimmed baking sheet. Arrange sole on sheet, flipping to coat in oil; sprinkle with one-third the garlic and season with salt and pepper. Broil until fish is opaque throughout, about 5 minutes.
Meanwhile, toss together remaining 2 tablespoons oil, remaining garlic, and tomatoes; season with salt and pepper. Cover and refrigerate half the tomato mixture for Tuesday. Stir cucumber, corn, and lemon juice into remaining tomato mixture. Serve fish with salad.