Cook the rice according to the package directions. Fluff it and stir in the lime zest, half the lime juice, the cilantro and 1/4 teaspoon of salt.
Mix the chili powder, cumin, garlic powder and 1/2 teaspoon of salt, and rub it over the chicken.
Heat the oil in a skillet over medium-high heat. Cook the chicken for 5–7 minutes per side, until it reaches 165°F (74°C) inside. Rest for 5 minutes, then slice. (For the vegetarian option, warm the black beans with the spices and a splash of water for 5 minutes.)
Toss the corn, tomatoes, red onion, remaining lime juice and a pinch of salt to make a quick salsa.
Warm the pinto beans with a pinch of salt.
Let everything cool, then divide the rice, chicken, beans and corn salsa among 4 containers. Pack lettuce, salsa and avocado separately.