Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil; add yams.
Bake in the preheated oven until yams are tender and wrinkled at the edges, about 20 minutes. Cool to room temperature, about 15 minutes
Bring water to a boil in a large saucepan. Add quinoa, stirring once; return to boil. Cook uncovered until water is absorbed, 10 to 12 minutes. Strain, shaking the sieve well to remove all moisture. Transfer to a mixing bowl.
Stir cucumbers, yams, parsley, olive oil, onion, lemon juice, red wine vinegar, salt, and pepper into the quinoa. Garnish with endive spears.