Preheat oven to 420 F. Prep a baking sheet by lining with foil and lightly greasing with olive oil.
In a medium saucepan, bring water to a boil. Add quinoa then cover the pan and reduce heat to low. Let cook 15-20 minutes until quinoa is cooked and water has been absorbed Set aside when done.
Meanwhile, in a large bowl, toss eggplant with roughly 2 tbs olive oil, balsamic vinegar, as well as salt and pepper to taste. Spread eggplant evenly over baking sheet and roast until it softens, about 20-25 minutes. Halfway through roasting, stir to flip the eggplant pieces.
Heat remaining 2 tbs olive oil in a large skillet. Add spinach and garlic, and sautée until spinach has slightly wilted. Remove from heat.
Once the eggplant has finished, add it to the skillet with the spinach. Lightly stir to mix, then add the quinoa and stir to evenly combine. Stir in feta, then add salt and pepper to taste.