Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
In a small saucepan, combine the dry quinoa with 0.5 cup of water, bring to a boil, then reduce heat and simmer covered for 15 minutes until fluffy.
Trim the woody ends off the asparagus spears and place them on one side of the prepared baking sheet.
Pat the flounder fillets dry with a paper towel and place them on the other side of the baking sheet.
In a small bowl, whisk together the olive oil, minced garlic, juice from the lemon, sea salt, and black pepper.
Drizzle the lemon-garlic mixture evenly over both the flounder fillets and the asparagus spears.
Bake in the oven for 12 to 15 minutes, or until the fish is opaque and flakes easily with a fork.
Fluff the cooked quinoa with a fork and plate it alongside the roasted asparagus and flounder fillets.
Garnish the entire dish with freshly chopped parsley and an extra squeeze of lemon if desired.