Mix together lime juice, agave nectar and 3 TB of oil for the marinade.
Add the strips to the marinade and marinate for an hour.
Cook the onions over medium heat in a skillet with a tablespoon of oil until tender, about 10 minutes, stirring frequently.
Once cool, mix the onions with balsamic vinegar and salt and pepper
Take the strips out of the marinade and pat to dry
If using a grill outside, sear the strips over direct heat for 2 minutes per side (you will know the grill is hot enough when you can only hold your hand 5 inches above the grill grate for no more than 3 seconds). When using an indoor grill, once you see steam rising off the skillet, you are ready to grease it with a little fat and begin searing.
Sear the strips over direct heat for 2 minutes per side, then move them off the heat, cover, and cook and extra 4 minutes (or until desired doneness).
Once cooked, leave the strips to rest for 5 minutes.
Mix the steak in a bowl with the greens, cilantro, tomatoes, avocados and dress with the 2 TB lemon juice and 3-4 TB of olive oil and salt and pepper to taste
