Season chicken breasts with salt, pepper, and a pinch of oregano.
Cook chicken in a skillet or on a grill over medium-high heat for 6-7 minutes per side until the internal temperature reaches 165F (74C).
Transfer chicken to a cutting board and allow to rest for 5 minutes before dicing into 1-inch cubes.
In a small jar, whisk together the olive oil, lemon juice, remaining oregano, salt, and pepper to create the dressing.
In a large mixing bowl, combine the chickpeas, cherry tomatoes, cucumber, and red onion.
For meal prep assembly, divide the baby spinach evenly into four airtight containers.
Top the spinach with the vegetable and chickpea mixture, then add the diced chicken and crumbled feta.
Store the dressing in four small separate containers to prevent the salad from becoming soggy.
Seal the containers and refrigerate for up to 4 days. Toss with dressing immediately before consumption.