Gently combine ground turkey, cheese blend, red pepper and onion in a large bowl. Shape into 4 patties about 1/2 inch thick. Place on a small cookie sheet lined with plastic wrap. Cover and refrigerate for 30 minutes to combine flavors.
Heat gas or charcoal grill to medium-hot. Using a long-handled brush, season rack with vegetable oil.
Grill patties, covered, for 4 minutes. Turn and grill 4 minutes longer or until patties register 165°F on an instant-read thermometer.
Place a tortilla on a flat surface. Mound 1/2 cup of lettuce on one half of the tortilla. Place a burger on the lettuce and top with 2 tablespoons of guacamole and 1/2 tablespoon of sour cream. Fold the tortilla in half, covering the filling. Repeat to make four burgers total and serve.
Place patties on a broiler pan and broil 4 to 5 inches from the heat for 8 minutes, turning once, or until they register 165°F on an instant- read thermometer.