Cut the chicken breast, red onion, and pineapple into uniform 1-inch cubes.
In a medium bowl, whisk together the tamari, toasted sesame oil, sweet Thai chili sauce, garlic powder, and ground ginger to create the marinade.
Add the chicken cubes to the marinade and toss to coat thoroughly; let sit for at least 15 minutes.
Thread the chicken, red onion, and pineapple onto skewers, alternating the pieces until all ingredients are used.
Heat a grill pan or outdoor grill over medium-high heat and lightly brush with olive oil.
Place the skewers on the hot grill and cook for 4-5 minutes per side, or until the chicken is cooked through and the pineapple is slightly charred.
Remove from heat, sprinkle with sesame seeds, and serve immediately.