In a small bowl, whisk together marinade ingredients. Place steak in a shallow container, and pour marinade over it. Refrigerate, covered, 8 hours or overnight to tenderize meat.
Drain the marinade from the meat. Grill the steak in a ridged grill pan over medium-high heat for 4 minutes each side. Transfer the steak to a cutting board and let stand.
In the same pan with the steak juices, add the bell peppers and onions. Saute the mixture for 3 minutes until the vegetables are limp. Thinly slice the steak against the grain on a diagonal.
Spread some guacamole on a tortilla, top with a few slices of steak, peppers and onions and salsa fresca. Roll up the tortilla to enclose the filling.
May also serve with sour cream and shredded cheese.