To prepare steak, combine 1 teaspoon oil and next 5 ingredients (through garlic) in a bowl. Rub steak with garlic-oil mixture; place in a large zip-top plastic bag. Seal; marinate in the refrigerator 1 hour, or overnight.
Lightly spray the rack of an outdoor grill with cooking spray. Heat to medium-high.
Heat remaining 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add onion, bell pepper, and jalapeño; sauté 5 minutes (A). Keep warm.
Place the steak on the grill, and cook 4 minutes on each side (without turning) for medium, or to desired degree of doneness (B). 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 (C) or fork until mixture is chunky.
Heat the tortillas in a covered casserole in a 300° oven until warm and pliable. Place a small amount of meat in each tortilla; top with the onion-pepper mixture and guacamole.