Preheat the oven to 425 degrees F (220 degrees C). Spray a baking dish with nonstick cooking spray.
Place potatoes, bell pepper, garlic, oil, and ½ teaspoon salt in the prepared dish; toss to coat.
Bake in the preheated oven for 30 minutes. Add tomatoes. Place tilapia filets on top of vegetables and sprinkle with remaining salt, pepper, and lemon zest.
Continue to bake until fish flakes easily with a fork, about 10 minutes.
Squeeze lemon juice over fish and serve.
