In a small saucepan, bring quinoa and water to a boil.
After the water begins to boil, reduce to a simmer and cover, allowing quinoa to absorb all water (about 1015 minutes).
Season the tilapia fillets with salt, pepper, and juice from half of the lemon.
Coat the bottom of a frying pan with 1 1/2 teaspoon of the olive oil and saute the tilapia over medium heat until the fish is opaque throughout and flakes easily (about 4 minutes on each side).
When the quinoa has absorbed all of the water, use a fork to fluff the quinoa and stir in the remaining 1 teaspoon of olive oil, cucumber, feta, and juice from the remaining 1/2 lemon.