In a large bowl whisk together the spices, lemon juice, olive oil and garlic. Add in the chicken and onions and give everything a good mix, making sure the chicken is well coated.
2 teaspoons smoked paprika, 2 teaspoons ground cumin, ½ teaspoons ground turmeric, ½ teaspoons ground cinnamon, ⅛ teaspoons ground nutmeg, 1 teaspoons freshly ground black pepper, 1 teaspoons salt, 4 tablespoons fresh lemon juice, ½ cup olive oil, 2 cloves garlic, 1 lb (about 500g) chicken breasts, 1 onion