1. In a spacious mixing bowl, thoroughly blend ground turkey with diced jalapeño, red onion, chili powder, cumin, salt, egg, and breadcrumbs, ensuring ingredients are evenly distributed without overworking the mixture.
2. Gently partition the seasoned turkey mixture into four uniform patties, carefully shaping them to maintain consistent thickness for balanced cooking.
3. Heat a grill or grill pan to medium-high temperature, lightly coating the cooking surface with oil to prevent sticking and promote beautiful sear marks.
4. Carefully position the turkey patties onto the heated surface, allowing them to cook undisturbed for approximately 6-7 minutes on each side until they achieve a deep golden-brown exterior.
5. Verify the internal temperature reaches 165°F (74°C) using a meat thermometer to guarantee safe consumption.
6. During the final cooking moments, crown each burger with a slice of pepper jack cheese, covering the grill to facilitate smooth melting and create a creamy, luxurious topping.
7. Transfer the perfectly cooked burgers onto a clean plate, immediately topping each with a generous dollop of fresh guacamole.
8. Select your preferred bun – whether a pillowy brioche or hearty whole wheat – and assemble the burgers with care.

When handling jalapeños, protect your hands with gloves or thoroughly wash them after preparation to prevent skin irritation.