Line a rimmed baking sheet with aluminum foil and spray with nonstick cooking spray. Set aside.
In a large mixing bowl, combine the chicken, panko, Parmesan, jalapeno, scallion, garlic, cilantro, mayonnaise, chili sauce, soy sauce, ginger, lemon juice and zest, and salt and pepper. Form your fingers into a claw and gently work the meat mixture until the ingredients are well-combined. If the mixture seems too wet to form into patties, add additional panko.
Wet your hands under cold running water, then form the meat into 8 patties, each an inch larger in diameter than the buns and about 3/4 inch thick. With your thumbs or a tablespoon, make a wide shallow depression in the top of each. Put them on the prepared baking sheet. Spray the tops with nonstick cooking spray. If not cooking right away, cover with plastic wrap and refrigerate.
When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes). Set the temperature to 350F and preheat, lid closed, for 10 to 15 minutes.
Arrange the burgers, depression-side down, on the grill grate. Remove and discard the foil on the baking sheet so you'll have an uncontaminated surface to transfer the sliders to when cooked.
Grill the burgers for about 25 to 30 minutes, turning once, or until they release easily from the grill grate when a clean metal spatula is slipped under them. The internal temperature when read on an instant-read meat thermometer should be 160F. (Stick the probe through the side of the burger for an accurate reading.)
In the meantime, spread the cut sides of the grilled buns with mayonnaise and arrange a tomato slice, if desired, and a few arugula leaves on one-half of each bun. Top with a grilled burger and red onions, if using, then replace the top half of the bun. Serve immediately.