Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the minced garlic and sauté for about 30 seconds until fragrant.
Add the diced red bell pepper, frozen peas, and carrots to the skillet. Stir-fry for 2-3 minutes until the vegetables are tender.
Push the vegetables to one side of the skillet and pour the beaten egg onto the other side. Scramble the egg until fully cooked, then mix it with the vegetables.
Add the cooked jasmine rice to the skillet, breaking up any clumps. Stir in the diced pineapple, soy sauce, oyster sauce (if using), sesame oil, black pepper, and crushed red pepper flakes. Cook for an additional 3-4 minutes, stirring frequently until everything is heated through.
Remove from heat and stir in the sliced green onions. Adjust seasoning if necessary.
Serve hot, garnished with fresh cilantro if desired.