Rub steak with garlic & olive oil mixture, place in a large zip-top plastic bag. Seal & marinate in the refrigerator 1 hour (or overnight).
Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add onion, bell pepper, and jalapeño, sauté 5 minutes & keep warm.
Place the steak on the grill, and cook 4 minutes on each side (without turning) for medium. Let stand 10 minutes on a cutting board before slicing crosswise into 1/3-inch-thick slices.
To prepare guacamole, combine all ingredients in a small bowl, and mix well, mashing with a pestle or fork until mixture is chunky.
Heat the tortillas & place a small amount of meat in each tortilla, top with the onion-pepper mixture and guacamole & enjoy!