Heat the oil in a large nonstick pan until shimmering. Add the chicken and the taco seasoning mix. Cook, turning frequently, until the chicken is done, about ten minutes.
Meanwhile, divide the spinach among four plates, or plastic boxes with lids if packing for work or school. Divide the beans, avocados, tomatoes, corn, cheese, and onion among the four dishes.
When the chicken is done, remove it from the heat to a cutting board and shred it into bite sized pieces. Divide the chicken among the salads. If you’re making the salads in advance, allow the chicken to cool before adding it to the dish.
Sprinkle the salads with chopped cilantro. Serve with a squeeze of lime juice and a drizzle of olive oil or salsa and sour cream if you prefer.
If preparing ahead of time, assemble salad but leave off lime juice, drizzle of oil, salsa, and sour cream.