How to Make It
Heat grill to medium-high. Once it is hot, clean the grill grate with a wire brush. Just before grilling, oil the grill grate.
Combine the bell peppers, onion, oil, and ¼ teaspoon each salt and black pepper in a medium bowl until coated.
Grill the vegetatables, covered, turning occasionally, until the peppers are charred and tender and the onion is tender, 5 to 7 minutes for the peppers and 12 to 14 minutes for the onion. Scrape the charred skin from the peppers with a paring knife and wipe clean with paper towels.
In a seperate medium bowl, gently mix together the pork, fennel seed, crushed red pepper, garlic, ½ teaspoon salt, and ¼ teaspoon black pepper with your hands until just combined. Form the pork mixture into four ¾-inch-thick patties. Use your fingers to make a shallow well in the top of each patty (this will prevent overplumping during cooking).
Grill the burgers until cooked through and an instant-read thermometer inserted in the center registers 145° F, 8 to 10 minutes per side.* During the last 2 minutes of cooking, top the burgers with the provolone and cook, covered, until melted. Grill the buns, split-side down, until toasted, 10 to 20 seconds.
Stack the burgers, peppers, and onion between the buns.
*This recipe includes the Real Simple test kitchen’s preferred cooking temperatures (considered safe by many experts) for burgers cooked to their juicy best. For maximum food safety, the U.S. Department of Agriculture recommends temperatures of 165° F for poultry, 145° F for fish, and 160° F for ground beef, lamb, and pork.