Preheat indoor or outdoor grill or oven broiler. Cook turkey bacon; cool, crumble and set aside. Chop tomatoes and set aside.
Grill chicken breast halves, turning to brown on both sides.
As soon as chicken comes off the grill, while it is still piping hot, top with a slice of Monterey Jack cheese, some crumbled bacon and chopped tomato; finally, sprinkle with shredded Cheddar cheese (the heat from the chicken will melt the cheeses and make this nice and gooey).
If you don’t get the cheese on the chicken in time to melt it, you can put it in the oven, under the broiler, for a few minutes.
Serve on a bed of baby spinach.