How to Make It
Preheat grill to medium-high (400°F to 450°F).
Spritz onion, bell peppers, zucchini, and squash all over with olive oil cooking spray, and sprinkle evenly with 1 1/2 teaspoons oregano. Place vegetables on oiled grates. Grill, uncovered, until soft and edges are browned, about 2 minutes per side for squash and zucchini and 5 minutes per side for onion and bell peppers. Remove from heat, and let cool. Chop vegetables into small pieces, and transfer to a large bowl.
Prepare orzo according to package directions for al dente, omitting salt. Reserve 1/2 cup cooking liquid. Drain and rinse under cold running water; stir orzo into vegetable mixture.
Add olives, vinegar, Parmesan, oil, lemon zest and juice, salt, black pepper, and reserved cooking liquid to orzo mixture; stir to combine. Gently stir in feta and remaining 1 tablespoon oregano.