Prepare the fajitas seasoning mix and set aside.
Cut the steak into 2-inch wide by 6-inch long strips.
Rub the steak strips with some of the prepared seasoning mix and set aside.**
Heat olive oil in a grill pan over medium-high heat and add pepper strips and sliced onions to the grill pan; season with salt, pepper, and a sprinkle of the fajitas seasoning mix.
Cook for about 4 to 5 minutes, or until tender.
Remove from heat and let cool for a minute.
Top each slice of steak with the vegetables; roll up and secure with a toothpick.
Heat up the grill pan again and add the roll-ups to the pan.
Cook until browned, about 2 to 3 minutes per side.
Remove from heat, remove toothpicks, and transfer to a serving plate.
Squeeze lime juice over the roll ups and garnish with chopped parsley or cilantro.
Serve with prepared guacamole.