Add the egg, shredded pepper jack, onion, garlic, cilantro, jalapeño, soy sauce, lemon juice, salt, smoked paprika, cumin, and black pepper to a large mixing bowl. Whisk or stir until well combined.
Add the ground turkey. Using clean hands, a silicone spatula, or a wooden spoon, gently mix until the seasonings are evenly distributed. Avoid overworking the meat.
Divide the mixture into 6 equal portions and form them into thick, compact patties, approximately 6 ounces (170 g) each.
Press a shallow indentation into the center of each patty with your thumb. This helps the burgers cook more evenly and maintain their shape.
Arrange the patties on a parchment-lined baking sheet or plate. Cover and refrigerate for at least 30 minutes or up to 24 hours.
When ready to cook, lightly grease the grill grates with a high-heat cooking oil and preheat the grill to high.
Place the chilled Jalapeño Pepper Jack Turkey Burgers on the hot grill. Close the lid and grill for approximately 5 minutes.
Carefully flip the patties and continue grilling for approximately 3 minutes, or until the centers reach an internal temperature of 165°F (74°C).
If using additional pepper jack cheese, place one slice over each patty during the final 30–60 seconds of cooking. Close the grill briefly to help the cheese melt.
Transfer the burgers to buns and finish with sliced jalapeño, spicy mayo, guacamole, tomato, lettuce, or your favorite toppings. Serve immediately.