Cook the grain (if using): Prepare quinoa or farro according to package directions. Spread on a plate to cool so it doesn’t wilt the veggies.
Make the dressing: In a small bowl or jar, whisk olive oil, lemon juice and zest, Dijon, garlic, oregano, salt, pepper, and red pepper flakes until emulsified.
Prep the vegetables: Dice cucumber, tomatoes, onion, and bell pepper.
Slice olives. Chop parsley and dill.
Combine the base: In a large bowl, add tuna, chickpeas, cooled grain, cucumber, tomatoes, onion, bell pepper, and olives. Flake tuna gently so it stays in bite-size pieces.
Toss with dressing: Pour dressing over the bowl and toss until evenly coated.
Taste and adjust salt, pepper, or lemon.
Add herbs and feta: Fold in parsley, dill, and feta. Don’t overmix—keep some texture.
Portion for meal prep: Divide into 4–5 containers. If adding greens, place them in a separate compartment or layer greens at the bottom and the salad on top.
Finish and chill: Add a lemon wedge to each container for a fresh squeeze before eating.
Chill for at least 30 minutes so flavors meld.