Preheat the oven to 375°. In a mortar, lightly crush the mustard and fennel seeds with the crushed red pepper. Set the pork tenderloins on a rimmed baking sheet and season them with salt and pepper. Spread the crushed spices on the baking sheet and roll the pork tenderloins in the crushed spices to coat them.
Roast the pork tenderloins for about 20 minutes, until an instant-read thermometer inserted in the thickest part of each tenderloin registers 145°. Transfer the pork tenderloins to a cutting board and let them rest for 10 minutes.
In a small bowl, mix the mustards with the honey and season with salt and pepper. Slice the pork 1/2 inch thick and serve with the honey mustard.