In a large skillet, heat the vegetable oil over medium heat. Add the ground beef and cook until browned, about 5-7 minutes. Drain excess fat if necessary.
Stir in the teriyaki sauce, garlic powder, ginger powder, salt, and pepper. Cook for an additional 3-5 minutes, allowing the flavors to meld.
In a separate bowl, combine the cooked rice, diced pineapple, and diced red bell pepper. Mix well.
To assemble the stacks, use a round mold or a small bowl. Layer the rice mixture at the bottom, followed by a layer of the teriyaki beef. Repeat the layers until the mold is full.
Carefully remove the mold and place the stack on a serving plate. Garnish with sliced green onions and sesame seeds if desired.
Serve immediately and enjoy your delicious Teriyaki Beef & Pineapple Rice Stack!