For the Pesto: Combine all of the pesto ingredients in a blender, and process until smooth and combined. (Turn off the motor, and scrape down the sides of the bowl as needed while processing.) For the Tilapia with Potatoes and Green Beans: Preheat the oven to 400 degrees.Place the potatoes in a saucepan covered with cool water; cover, and bring to a boil over high heat. Reduce the heat and simmer until tender, about 12 to 15 minutes. (Hint: A fork inserted into the center of a potato should slide in and out with ease.)Meanwhile, place the green beans in a steam basket set over a pot of boiling water. Steam the beans until crisp-tender, about 10 to 12 minutes. Hold warm.Place the tilapia fillets on a baking pan coated with cooking spray. Spread 1 tablespoon of pesto evenly over the top of each fillet. Bake in the preheated oven until just cooked through (flakes easily with a fork), about 15 minutes.Serve the tilapia with 1/4 of the steamed green beans and potatoes; drizzle 1 tablespoon of sour cream over the potatoes, and garnish each plate with a lemon wedge. Serve immediately.