Rinse the rice under cold water for 2–5 minutes until the water runs clear, then soak for at least 5 minutes.
Bring 3.5 cups water to a boil in a large saucepan, add the rice, cover, reduce to low, and simmer for about 10 minutes until the water is absorbed and rice is tender.
Remove the pan from heat, stir in 2 tablespoons butter, then fold in the minced cilantro and 1/2 lime juice just before serving.
In a medium bowl, combine the chicken breasts, 2 tablespoons olive oil, 1/2 lime juice, and 2 tablespoons taco seasoning; cover and refrigerate to marinate for 15 minutes up to 24 hours.
Preheat a grill, grill pan, or skillet over medium-high heat. Grill the chicken 5 minutes per side until cooked through, then remove and set aside to rest.
Using the same pan, add the sliced bell pepper and sliced onion and sauté 1–2 minutes until slightly softened and charred; remove from heat.
Make the tomato salsa: in a medium bowl combine the diced plum tomatoes, 1/4 cup finely diced red onion, 2 tablespoons minced cilantro, 1 tablespoon lime juice, and salt and pepper to taste; chill until ready to serve.
Slice or dice the cooked chicken into bite-size pieces.
Assemble bowls: divide the cilantro-lime rice among bowls, top each with about 1/2 cup chicken, grilled peppers and onions, tomato salsa, chopped romaine, black beans, corn, and a dollop of sour cream.