Step 1

Preheat the oven's broiler and set the oven rack about 6 inches from the heat source. Line a baking sheet with aluminum foil. Cut the red bell pepper in half from top to bottom; remove the stem, seeds, and ribs; place pepper cut-side-down onto the prepared baking sheet.

Step 2

Cook under the preheated broiler until the skin of the pepper has blackened and blistered, about 5 minutes. Allow the blackened pepper to cool and steam in a paper bag for 5 minutes; peel and dice; set aside.

Step 3

Stir together the 2 ounces feta cheese, mayonnaise, lime juice, the 1 sprig chopped mint, and the 1 sprig chopped parsley in a small bowl; set aside.

Step 4

Preheat an outdoor grill for medium heat, and lightly oil the grate.

Step 5

Place the roasted red pepper, ground beef, feta cheese, spinach, bread crumbs, egg, garlic, onion, basil, the remaining mint, and the remaining parsley in a bowl. Sprinkle with salt and pepper, and mix gently with your hands until evenly combined. Divide the meat mixture to form 4 equal 4 1/2 inch patties.

Step 6

Cook on the preheated grill until the burgers are cooked to your desired degree of doneness, about 4 minutes per side for medium. An instant-read thermometer inserted into the center should read 160 degrees F (70 degrees C). Serve burgers on warm toasted Kaiser roll with the feta cheese spread, fresh tomatoes, and lettuce.