In a large zip-top plastic bag, add all the marinade ingredients.

Place the skirt or flank steak into marinade in the zip-top plastic bag. Close and turn and shake the bag to get the marinade to cover the entire steak.

Refrigerate for 1 or 2 hours but no more than 2 hours due to the pineapple juice in the marinade. You don't want the steak to get too mushy due to marinating too long.

Remove the steak from the marinade and let marinade drain off the steak.

Prepare grill for cooking, or if cooking on top of the stove, add about a tablespoon of oil to a skillet or grill pan and place over medium-high heat.

Grill or cook the fajita meat for about 6 - 8 minutes and then turn and grill on the other side for another 6 - 8 minutes or until cooked to your preferred level of doneness.

Remove the steak from the grill. Cover with foil and set aside for now.

If cooking on the stove, add the sliced onions, and red and green peppers to the same pan that you cooked the fajita meat and cook 3 - 5 minutes over medium heat.

If grilling, spray a vegetable grilling rack with cooking spray and add the sliced vegetables. Grill the vegetables for 3 - 5 minutes or until the onions are soft and slightly browned on the edges.

Remove the vegetables and place them on a plate covered with foil. Set aside.

Heat the flour tortillas either on the grill or stove for per package instructions, or microwave for 30 seconds.

Place the fajita meat on a cutting board and slice the meat against the grain into thin slices. It is very important to slice against or across the grain, otherwise, the meat may be tough.

Place the sliced fajita meat and vegetables on a platter and serve the Tex-Mex Beef Fajitas with warm tortillas.

Enjoy!