1. Place a cast-iron pan over medium-high heat and heat the rendered bacon fat (ideally, use the pan you just made the bacon in). Add extra canola oil if necessary; oil should coat surface of pan.
2. In a large bowl, combine the chicken, bacon, scallions and 1/2 of the Dijon mustard and season with salt and pepper. Mix until just blended. Test flavor by cooking a small portion of mixture.
3. Form 4 burger patties about 1 inch thick. Sear the burgers, turning once, until done, about 3-4 minutes per side. Be sure that burger is cooked all the way through since this is chicken — should be 165 degrees F in the center of the burger.
4. Meanwhile, arrange tomato slices on a large plate and season them with salt and pepper.
5. In a medium bowl, combine the remaining Dijon mustard, jalapenos and mayonnaise and mix well.
6. Spread spicy mayo on bottoms and tops of buns. Place shredded romaine on bun bottom and top with tomato slice, add the burgers and top with a second tomato.
7. Finish with the bun tops and serve.
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