In a blender, whirl parsley, olive oil, 2 tbsp. lemon juice, zest, and 1/4 tsp. salt.
In separate bowls, gently toss potatoes and squash with some dressing, and tomato wedges with 1 tsp. lemon juice, adding salt and freshly ground black pepper to taste.
On 4 plates, evenly divide veggies and trout. Add more dressing to taste.