Combine all of the ingredients except for the chicken breasts in a 1-gallon freezer bag. Close the bag and squish the marinade around to mix. Add the chicken and massage the marinade into the meat until evenly coated. Seal the bag and place it in a bowl in the refrigerator (the bowl protects against leakage); marinate for at least 6 hours or overnight.
Clean the grill and preheat to high. Lightly dip a wad of paper towels in vegetable oil and, using tongs, carefully rub over the grates several times until glossy and coated. (Alternatively, you can spray the grates generously with a non-flammable cooking spray.) Place the chicken on the grill and cook, covered, for 2-3 minutes per side, turning only once. Transfer to a cutting board and slice into bite-sized pieces.
For the Green Sauce
Combine all of the ingredients in a blender or food processor and blend into a smooth sauce. Taste and then blend in some of the reserved jalapeño seeds to add heat, if desired. Taste and adjust seasoning if necessary. Transfer the sauce to a bowl, cover, and refrigerate until ready to serve.
For the Quinoa
Add quinoa, salt and 2-2/3 cups water to a medium saucepan. Bring to a boil and then reduce heat to low, cover, and cook for 15 minutes, until the water is absorbed and the quinoa is cooked. You’ll know it is done when the little “tails” sprout from the grains. (If necessary add 1-2 tablespoons more water if the quinoa is not cooked by the time all the liquid is absorbed.) Transfer to a serving bowl.
Scoop warm quinoa into bowls and top with grilled chicken, optional toppings, and green sauce.
Note: After touching the seeds of the jalapeño pepper, be sure to wash your hands well and avoid touching your eyes.
Note: Nutritional information was calculated assuming that approximately 3 Tbsp. of the oil is absorbed by the chicken while marinating.