1. Season chicken with salt and lemon juice. In a bowl put salt, oregano, achiote, vinegar, cumin, and garlic; mix well. Add chicken and marinate for 2 hours. Drain and fry chicken in a skillet until browned.
2. In a heavy saucepan place the browned chicken, half of the onions and half tomatoes; another layer of chicken, onions and tomatoes. Sprinkle with salt and pepper. Cover the saucepan and simmer for 1 hour or until tender.