Prepare a grill or large grill pan for medium-high heat. Mix the brown sugar, 1 tablespoon salt and 2 teaspoons pepper together in a small bowl. Rub the mixture into the steaks and set aside for 15 minutes.
Put the tomatoes in a large mixing bowl. Sprinkle with salt and pepper and let sit at room temperature while you prepare the rest of the ingredients.
Whisk together the sour cream, cumin, lime zest and juice and a pinch of salt and pepper in a small bowl and set aside.
Meanwhile, lightly oil the grill grates. Brush the corn and onions liberally with the oil, sprinkle with salt and pepper and put on the grill. Grill the corn until lightly charred, turning the ears occasionally, and the onions until charred and tender, flipping as needed, 6 to 8 minutes for both. Transfer the vegetables to a cutting board to cool slightly.
Grill the steaks until crisp, about 4 minutes per side for medium rare. Set aside to rest for 5 minutes.
While the steaks rest, cut the corn away from the cobs and quarter the onion rounds. Add the corn, onions, black-eyed peas and half of the parsley to the bowl with the tomatoes and toss gently to combine. Season with salt and pepper.
Slice the steaks across the grain and divide among 4 plates. Divide the succotash among the plates, top with a dollop of the reserved sour cream mixture and garnish with the remaining parsley or cilantro. Serve immediately.
Copyright 2014 Television Food Network, G.P. All rights reserved.