Taste and add salt if necessary (feta and olives are salty to begin with, so you may not need any).
In a medium bowl, mix together the filling (cooked quinoa, feta, artichokes, olives, olive oil and garlic).
Core the tomatoes by slicing off the top ⅛ inch of each tomato. Run a small knife vertically around the core. Be careful not to cut through the bottom. Use your finger to gently pull out the core and use the knife to clean out any excess left inside.
Preheat oven to 375 degrees Fahrenheit
Cook your quinoa: Measure out ⅓ cup of quinoa, pour into a mesh colandar, and rinse the quinoa under running water for a minute. Pour the rinsed quinoa into a small pot and add ⅔ cup water (you're going for a 1:2 ratio of quinoa and water). Bring to a boil, then cover and simmer for 15 to 18 minutes. Remove from heat, let sit for a few minutes, and fluff with a fork. ⅓ cup uncooked quinoa should yield a little over one cup cooked quinoa. I would use all of it in the filling.