In large zip lock baggie (or bowl), combine together: olive oil, garlic, smoked paprika, cumin, cinnamon, salt, pepper, lemon juice, and pepper flakes.
Place chicken breasts into marinade and place in 'fridge, marinade for at least an hour (preferably longer).
Peel and slice onions and place into large oven proof baking dish. Place chicken on top of onion slices. Pour any remaining marinade into baking dish. If needed add a drizzle of olive oil to make sure onions are well coated (so they don't burn).
Place baking dish into preheated 425* oven and bake for 50-60 minutes, depending on size of chicken breast. Chicken should be well browned.
For Sauce:
Combine all ingredients in small bowl and refrigerate for at least one hour. If sauce seems a little thick, add a little more lemon juice.
Serve chicken with roasted onions and a big spoonful of the Garlic Tahini Sauce. *Optional: top with chopped parsley and lemon wedges.
Enjoy!