Mix together olive oil, lime juice, cilantro, garlic salt, paprika, pepper, and cumin in a bowl. Reserve 2-3 tablespoons in a separate bowl (for basting). Place the beef in a large ziploc bag and pour the marinade over the meat. Marinate in refrigerator for 1 hour.
Mix together chopped peaches, tomato, bell pepper, and cilantro. Add in lime juice, agave, and salt to taste. Cover and refrigerate.
Alternate onions and steak pieces on skewers when ready to grill. Grill for 5-8 minutes until meat is done but still juicy and tender, basting with the marinade mixture every 1-2 minutes. (Remove onions and grill for longer if softer onions desired.)
Serve skewers with a large helping of peach salsa and rice. Enjoy!