Cut the onions into fourths removing the outer layer, then removing the layers into sections. Cut the bell pepper into fourths removing the seeds and inner layers. Cut the bell pepper into eight pieces. Cut the fajita steak into about 1/2-inch-thick strips measuring about 3 to 4 inches long.
In a large skillet grill the onions on high until they are half white and half clear. Then add the steak and shrimp. Once the steak is brown on both sides and the shrimp is starting to turn orange add the sliced lemons, the seasonings and the bell pepper pieces. Cook until shrimp and steak are fully cooked - it may take 5 to 15 minutes.