Soak wooden skewers in water for at least 20 minutes to prevent them from burning on the grill.
In a small mixing bowl, whisk together the defatted peanut powder, ground ginger, garlic powder, onion powder, cayenne pepper, smoked paprika, sea salt, and black pepper to create the Yaji spice blend.
Slice the sirloin steak into uniform 1-inch cubes and place them in a large bowl.
Drizzle the beef with avocado oil and toss until every piece is lightly coated.
Sprinkle the Yaji spice blend over the beef, tossing thoroughly until the meat is completely encrusted in the nutty seasoning.
Cut the red onion and bell pepper into 1-inch chunks suitable for skewering.
Thread the seasoned beef cubes onto the skewers, alternating with the red onion wedges and bell pepper pieces.
Preheat a grill pan or outdoor grill to medium-high heat.
Place the skewers on the hot grill and cook for 3-4 minutes per side, turning occasionally, until the beef is cooked to your preference and the vegetables are slightly charred.
Remove from heat and let the beef rest for 2 minutes before serving hot.