Chop the vegetables into uniform pieces. Transfer to a large bowl and set aside.
Prepare the marinade by combining 1/2 cup olive oil, 1 teaspoon dried oregano, and 1/2 teaspoon each salt, pepper, onion powder and garlic powder. Whisk well; drizzle over the chopped vegetables and toss to coat.
Spread the vegetables on 2 large, rimmed baking sheets lined with foil. Roast at 400° for 10-15 minutes, tossing halfway through, until tender-crisp.
Cook the orzo according to package instructions. Drain, then transfer to a large mixing bowl.
Prepare the dressing by combining 1/2 cup olive oil, 6 Tablespoons lemon juice, 2 teaspoons lemon zest, 1 1/2 Tablespoons dijon mustard, 1/2 teaspoon salt and 1/2 teaspoon pepper. Whisk well.
Place the shrimp in a small mixing bowl or gallon size ziploc bag. Pour 1/3 cup of dressing over the shrimp and toss to coat.
Combine the cooked orzo with the roasted veggies, seasoned shrimp, crumbled feta, chopped dill and parsley, and remaining dressing. Toss until well combined.
Enjoy immediately or refrigerate for later.