To Make Chipotle Chicken: 

1. In a small bowl, mix together chipotle chili powder, cumin, salt, chili powder, and black pepper. Rub both sides of the chicken breast cutlets with the spice mixture. 
2. Heat olive oil in a large skillet over medium heat. Once the oil starts to shimmer, add the chicken breast. Do not overcrowd the pan. Work in batches if needed. Cook chicken for 5-7 minutes on each side, or until the internal temperature reaches 165 degrees.  
3. Let the chicken cool for a few minutes and slice into 1/2-1/4 inch strips. 

To Assemble the Sandwich: 

1. Brush olive oil on one side of the bread and spread mayo (1/2 tbsp) on the other side. Take four slices of bread and add cheddar cheese (2 tbsp), chicken, tomatoes, and onion to the side with mayo. Top it off with more cheddar cheese. Now place a slice of bread on top (Mayo side down, olive oil side up).
2. Heat a large skillet to medium-low and add the sandwiches to the skillet. Cook for 4-7 minutes or until the bread starts to toast. Then flip and cook another side. Serve immediately.