Preheat oven to 425°. In a bowl, toss zucchini and onions with 1 tablespoon olive oil and 1/4 tsp each salt and pepper. Spread on 2 baking sheets. Roast until tender (about 15 minutes), stirring once. In a food processor or blender, process arugula, garlic, walnuts, 1 tablespoon lemon juice, lemon zest, Parmesan, and 1/4 tsp each salt and pepper, pouring in 3 tablespoons olive oil in a slow stream. In a large bowl, toss arugula pesto with penne, roasted vegetables, grape tomatoes, and 2 tablespoons lemon juice.