Toss the eggplant, bell peppers, onion, and garlic with the olive oil, salt, and pepper on a large sheet pan. Roast for 40 minutes, until browned, turning once with a spatula.
Meanwhile, cook the orzo in boiling salted water for 7 to 9 minutes, until tender. Drain and transfer to a large serving bowl. Add the roasted vegetables to the pasta, scraping all the liquid and seasonings from the roasting pan into the pasta bowl.
For the dressing, combine the lemon juice, olive oil, salt, and pepper and pour on the pasta and vegetables. Let cool to room temperature, then add the scallions, pignolis, feta, and basil. Check the seasonings, and serve at room temperature.