Preheat a large skillet over medium-high heat. Add oil and heat until shimmering. Add chicken breast, cook until completely cooked through and browned on both sides. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Remove chicken from skillet, tent loosely with foil to keep warm and set aside.
Return skillet to heat. Add onion and cook for 3-4 minutes, stirring occasionally. Add garlic and cook one more minute. Stir in roasted and chopped poblano pepper. Remove from skillet and set aside.
In same skillet, place corn, water, buttery spread (if using) and contents of rice package. Bring to a boil, cover and reduce heat. Simmer for 7 minutes or until water has been absorbed and rice is tender. Add onion mixture back to skillet and toss together.
Place rice mixture on a serving platter. Slice chicken and place on top of rice (or chop into bite-sized pieces and stir into rice, then plate). Serve immediately.
To roast a poblano pepper, preheat oven to 500 degrees F (260 degrees C) and place poblano pepper on a foil-lined baking sheet. Bake, turning occasionally, until skin is charred, about 30 minutes. Place pepper in a paper bag for about 5 minutes to make skin removal easier.