Cook the quinoa according to the package directions, and let it cool to room temperature.
In a mixing bowl, mash the chickpeas using a potato masher, fork, or the back of a large spoon. Add the cooked quinoa, garlic, scallions, parsley, lemon zest, olive oil and Sriracha (if using) to the mashed chickpeas. Season the mixture with salt to taste.
Transfer the falafel mixture to a food processor or blender, and pulse a few times until the ingredients hold together a bit. You don’t want a puree, you just want a coarse "dough" that will stick together.
Use your hands to form the falafel mixture into tablespoon-sized balls. You should have enough for about a dozen small falafel. Briefly set aside while you make your relish.
Combine all of the ingredients for the relish in a small bowl. Set aside while you cook your falafel.
Heat 2 tablespoons olive oil in a large non-stick skillet over medium-high heat. When the oil is hot, add the falafel and cook for about 3 minutes per side (you can gently press each ball down with the back of a spatula to form a thick pancake if it makes things easier.) Remove falafel to a paper towel-lined plate to drain any excess oil.
Serve the falafel warm with relish and yogurt-tahini dressing. If you’re not afraid of a little gluten or judgment from Gwyneth, I recommend stuffing everything in a warm pita and going to town.