Toss onions with 2 tablespoons lime juice in medium bowl. Season with salt if desired. Let stand, tossing occasionally, until wilted, about 30 minutes.
Season pork, if desired, with salt and pepper. Melt 1 tablespoon Country Crock® Spread in large nonstick skillet over medium-high heat and cook pork, turning once, until done, about 3 minutes. Remove and set aside.
Add remaining Spread, plantains and all but 1/4 cup onions to skillet and cook over medium-high heat, stirring frequently, until plantains are lightly browned and onions are softened slightly, about 2 minutes. Remove from heat and stir in tomatoes, mango, cilantro and remaining 1 tablespoon lime juice.
Top pork with plantain mixture, then sprinkle with remaining lime marinated onions. Serve with rice and black beans on the side and if desired, lime wedges.