In a large bowl or resealable plastic bag, add the chicken and the next nine ingredients (all the seasonings, etc.). Marinate in the fridge for four hours. I have marinated it for less time but the longer you marinate the more the flavor is infused.
Preheat grill to medium heat and oil the grate. Grill chicken 4-5 minutes per side or until chicken is no longer pink. Top with shredded cheese and diced tomatoes. You can either do this on the grill by laying some foil on the grill, transferring the chicken to the foil, and topping with cheese and tomatoes. Close the grill lid to let the cheese melt for a couple of minutes. You can also just remove the grilled chicken and top with cheese and tomatoes. You could pop it in the microwave, broil in the oven, or just let the heat of the chicken melt it. Garnish with additonal cilantro if desired.
Notes
I really prefer my chicken breasts thin. I buy chicken from Costco and slice them lengthwise into two thinner breasts.