Chicken and Yellow Pepper Sauce Sandwiches

1/2 c sweet paprika
2 tblsp kosher salt
2 tblsp garlic powder
1 tblsp dried thyme
2 tsp ground celery seed
2 tsp ground black pepper
2 tsp cayenne pepper
chicken breasts, brined (if desired) and pounded to an even thickness
2 medium onions, chopped
1 yellow bell pepper, chopped
1 celery rib, chopped
4 garlic cloves, minced
2 tblsp olive oil
a 28-ounce to 32-ounce can plum tomatoes, drained and chopped
1 cup chicken broth
1 tsp minced fresh thyme leaves
1-2 tblsp butter, softened, or more if making a lot of sandwiches
1-2 cloves garlic, minced, or more as needed [the more garlic the better of course]
1 loaf of French bread

Combine all the spices to create a rub for the chicken. Rub all over the breasts and set aside for at least an hour and preferably several to allow the flavors to penetrate. There will be plenty of spice rub left over, which you can store in an air-tight container.
In a heavy saucepan cook onions, bell pepper, celery, and garlic in oil over moderately low heat, stirring occasionally, until celery is softened.
Add tomatoes, broth, and thyme and simmer sauce 25 minutes, or until most of liquid is evaporated.
Season sauce with salt and pepper. It will be very chunky, like a salsa.
Grill the chicken breasts.
Slice the French loaf in half lengthwise. Combine the softened butter and garlic and spread all over both sides of however much bread you need. Put in the oven on a pan at 350 degrees until it looks toasted and yummy. Sometimes I use the broiler if things aren't moving along fast enough.
Assemble sandwiches: put a chicken breast on the bottom piece of garlic bread, then lots of the yellow pepper sauce, then the top half of the garlic bread. Serve with a spoon to scoop up all of the sauce.

Source: epicurious.com (yellow pepper sauce) and Cook's Illustrated, July & August 2002 (spice rub)