For the pork, combine the fennel pollen, garlic powder and crushed red pepper. Rub spice mixture all over the tenderloins and season generously with salt. Let sit for at least 1 hour… it’s even better if you let it hang out overnight.
For the relish, preheat a grill to medium-high heat. When the grill is hot, brush the grill a wire grill brush to clean then brush grates with a towel soaked with oil.
Place the soaked broccoli rabe on the grill, keeping the excess water on the broccoli rabe to help it steam and cook through without charring it too much. When the broccoli rabe is charred and the stems are cooked through, about 5-7 minutes, remove it and toss with olive oil and salt. Coarsely chop and reserve.
Toss the onion slices with salt and olive oil. Place onions on the grill and cook until the onions are charred and very soft, about 8-10 minutes. Remove from the grill, coarsely chop and add to the reserved grilled broccoli rabe.
Toss the julienned cherry peppers in with the onions and broccoli rabe. Season the mix with the cherry pepper juice and olive oil, and taste to make sure it is delicious. This can TOTALLY be done ahead.
Rub the seasoned pork tenderloins with olive oil, ,place them on the preheated grill and cook about 3-4 minutes on all sides. Remove and let rest for about 8-10 minutes before slicing.
To assemble the sammies, slice the pork tenderloins on the bias into slices about 1/4-inch thick. Cut the sandwich rolls in half but not all the way through so they open like a book. Scoop the bready part out of the top of the roll and toast face-down on the grill for 2-3 minutes.
Divide the sliced pork between the toasted rolls and arrange in an even layer. Lay 2 slices of provolone on top of the pork on each sammy, spread some broccoli rabe relish on top of the cheese and sprinkle with grated Parmigiano. Close up the rolls and serve warm or at room temp.