Gather all ingredients and prepare them according to specifications: dice the tomato into 1/2-inch pieces, slice the cucumber into 1/4-inch half-moons, finely dice the red onion, slice the kalamata olives, rinse and drain the chickpeas, and cube the cooked chicken into 1-inch pieces. Chop the romaine lettuce into bite-sized pieces. Measure out the Greek vinaigrette, lemon juice, feta cheese, and dried oregano. Having everything prepped and ready before assembly ensures smooth layering and prevents the jar from sitting open too long.

Start by pouring the Greek vinaigrette into the bottom of a 32-ounce mason jar, then add the lemon juice and sprinkle the dried oregano over it—this creates a flavorful dressing base. Layer the heavier, sturdier ingredients next: add the diced tomato, followed by the sliced cucumber, then the chickpeas, then the red onion, then the sliced olives. I like to layer the feta cheese next because it won't dissolve into the dressing, creating a barrier between the wet and dry ingredients. Add the cubed chicken on top of the cheese. Finally, top with the chopped romaine lettuce, pressing down gently so the jar closes properly. The lettuce sits above the dressing line, staying crisp until you're ready to eat.

Screw the lid tightly onto the mason jar. The salad can be refrigerated for up to 3 days. When you're ready to eat, shake the jar vigorously for 10-15 seconds to distribute the dressing throughout all the ingredients, then pour the entire contents into a bowl or onto a plate and enjoy.