Add the quinoa, cayenne, and remaining 1/2 teaspoon salt and 1/4 teaspoon chili powder. Stir to coat the quinoa with the oil and let brown for 2 minutes. Pour in the chicken stock, then increase the heat to high and bring the broth to a boil. Once boiling, cover and reduce the heat to a simmer. Let simmer until the quinoa is tender, 12 to 15 minutes. Uncover and fluff with a fork. Zest the lemon directly into the pan, then juice the lemon and add the lemon juice and parsley to the skillet as well. Toss to combine, then top with the reserved shrimp. Sprinkle with additional fresh parsley. Serve warm.