Rinse the trout and dry with the paper towels. Open the trout, lie flat, and season the cavity with the salt and pepper.
Spray a nonstick skillet with the cooking spray. Sauté the leeks and garlic over low heat for approximately 4 minutes. Increase the heat to medium and mix in the chicken broth and thyme leaves. Cook, stirring often, until almost all of the liquid has been absorbed.
Stuff the cavity with the mixture and close the trout. Set the trout in a shallow baking dish. Bake for approximately 15 minutes.
Mix together the fat-free sour cream, parsley, thyme, and pepper. Once the trout are done cooking, take the heads and tails off and throw away. Drizzle the sour cream mixture on top.