In small bowl, whisk or stir together sauce ingredients until completely combined. Set aside.
In small frying pan, add 2 tablespoons butter and melt over medium to medium-low heat. Add mushrooms and sauté until browned on both sides. Season with salt and pepper, and 1 Tbl. of the sauce, for one minute longer. Remove to a small plate or bowl with a slotted spoon.
Add more butter if needed, add paprika, stir, then add turkey breast slices, turning to coat. Only cook long enough to warm. Spread tops with some of the sauce, saving the rest to spread on the bread.
Spread one side of each slice of bread with the sauce. Top bottom slice of bread with shredded cheese, then one or two slices havarti cheese. Top with slice(s) of smoked turkey spread with more sauce, then add mushrooms, then bacon pieces. Top with another slice or two of havarti, and more shredded cheese. Place other slice of bread on top, sauced side down. *Or don't assemble completely, and place the second slice of sauced and cheese-topped bread onto the griddle to get it started. Then place it on top.
Place 1 - 2 Tbl. butter onto heated frying pan or griddle and melt. Then place sandwich onto griddle, and toast bottom (and top if doing them separately), over medium to medium-low heat. When time to turn, move sandwich to the side of the pan, add more butter, turn sandwich carefully placing it into the new pool of melted butter, and toast other side. *Do not cook over too high of heat, or cheese won't have time to melt. Toast slowly. Turn several times more if needed.
When bread is nicely toasted and cheese has melted, remove to a cutting board, and slice in half corner-to-corner. Serve hot, and enjoy!!
Leftover smoked or roast chicken or turkey can be used, or you can purchase a rotisserie chicken from your local store.