Combine cooled quinoa, chopped spinach, crumbled feta, eggs, breadcrumbs, garlic, diced onion, salt, and pepper in a large bowl until well-blended, about 1 minute stirring.

Cover the bowl with plastic wrap and refrigerate for 10 minutes to firm up the mixture, making it easier to shape patties without sticking.

Scoop roughly ⅓ cup of mixture for each patty, shaping into 12 even discs. Place them on a parchment-lined tray, gently pressing edges to seal.

Warm 2 tablespoons of olive oil in a large nonstick skillet over medium heat until shimmering, about 2 minutes, ensuring a crispy crust later.

Place patties in skillet, cooking 3–4 minutes per side or until golden brown. Flip gently with a spatula to maintain shape and even browning.

Transfer patties to paper towels for 2 minutes to absorb excess oil. Serve warm with lemon wedges or tzatziki sauce alongside.