Using pre-cooked chicken makes this a fast, easy, and delicious no-cook meal. I like to make pesto and keep it in the freezer for meals like this. A bit of finely chopped red onion and fresh herbs would also be a nice addition here.
Combine the lemon juice, zest, olive oil, salt, pepper, and monk fruit, if using in a large bowl. Add the mixed greens and toss to coat evenly. Top with tomato, cucumber, feta, and pesto chicken and serve.