Drain the tuna well. Press the lids against the tuna to remove as much liquid as possible.
This keeps the mixture from getting watery later.
Make the dressing. In a bowl, whisk Greek yogurt, Dijon, lemon juice, lemon zest, olive oil (if using), 1/2 teaspoon salt, 1/2 teaspoon pepper, and a pinch of garlic powder. Taste and adjust acidity or salt.
Prep the crunch. Finely chop celery, red onion, cucumber, and parsley. Keep pieces small so each bite is balanced.
Combine the tuna mix. In a large bowl, flake the tuna with a fork.
Fold in the dressing, celery, onion, parsley, and optional pickles or capers. Stir gently so it stays light.
Layer your base. Divide greens and cooked quinoa or cauliflower rice into 4 meal-prep containers. Keep greens dry if you can—they stay crisp longer.
Add the tuna. Spoon the tuna mix evenly over each container.
Top with cucumber and tomatoes. If you like heat, add a pinch of red pepper flakes.
Finish and taste. Add a final squeeze of lemon or a light sprinkle of salt. This lifts the flavors.
Seal and chill. Close containers and refrigerate.
For best texture, add the tomatoes fresh on the day you eat, but they’re fine stored if you dry them well.