In a small bowl, combine 2 tablespoons oil, lime juice, garlic, cumin and oregano.
Pour half in a large resealable plastic bag; add chicken. Seal bag and turn to coat. Marinate for at least 30 minutes. Cover and refrigerate remaining marinade.
In a large skillet, heat remaining oil on medium-high. Saute onion for 2-3 minutes or until crisp-tender.
Drain and discard marinade. Add chicken to skillet; stir-fry until meat is no longer pink. Add the red pepper, chilies and reserved marinade; cook 2 minutes or until heated through. Stir in almonds.
Serve immediately over shredded lettuce; top with tomatoes and avocado.