Cook couscous in water as directed on package, omitting oil; cover to keep warm.
Meanwhile, in 1-quart saucepan, mix flour, 1/4 teaspoon salt, the thyme and milk until smooth. Cook over medium-high heat, stirring constantly, until bubbly and thickened. Remove from heat. Stir in butter-flavor granules and lemon peel until well blended; cover to keep warm.
Sprinkle both sides of turkey breast slices with 1/4 teaspoon salt and the pepper. In 10-inch nonstick skillet, melt butter over medium-high heat. Add turkey; cook 2 to 3 minutes, turning once, until no longer pink in center. Serve turkey slices with sauce over couscous; sprinkle with parsley.