Preheat oven to 400°F and tear 4 large pieces of parchment paper; divide zucchini slices and halved cherry tomatoes among centers and top each with a tilapia fillet.
Scatter kalamata olives over fish, drizzle with olive oil and lemon juice, sprinkle with oregano and salt, then fold parchment to seal each packet.
Place packets on a baking sheet and bake for 15 minutes until fish flakes easily.
Carefully open packets and serve each with the vegetables and pan juices.