Cook shrimp: Pat shrimp dry; season with a pinch of salt, pepper, and a little oregano. Heat olive oil in a skillet over medium-high and sear shrimp 2–3 minutes per side until pink with light golden edges. Cool slightly.
Prep veggies: Dice cucumber and bell pepper; halve tomatoes; thinly slice red onion; chop parsley and dill.
Make dressing: Whisk lemon juice, zest, garlic, Dijon, oregano, salt, and pepper. Slowly drizzle in olive oil while whisking until emulsified.
Assemble: In a large bowl, combine chickpeas with half the dressing. Add shrimp and vegetables; toss gently. Add remaining dressing to taste.
Finish: Fold in feta (if using). Taste and adjust lemon/salt/pepper. Serve right away or chill 15–20 minutes.