Prepare the Sauce: In a small bowl, whisk together the soy sauce, pineapple juice, white vinegar, coconut sugar (or brown sugar), and cornstarch until smooth. Set aside.

Cook the Beef: Heat 1 tablespoon of olive oil in a large skillet or wok over medium-high heat. Add the beef strips, season with salt and pepper, and stir-fry for 3-4 minutes until browned and cooked through.

Sauté the Vegetables: In the same skillet, add the remaining tablespoon of olive oil. Add the sliced onion and garlic, and sauté for 2-3 minutes until the onion is softened and the garlic is fragrant. Add the broccoli florets and stir-fry for an additional 3-4 minutes until the broccoli is bright green and crisp-tender.

Combine Beef and Pineapple: Return the cooked beef to the skillet with the vegetables. Add the pineapple tidbits and stir to combine.

Add the Sauce: Pour the prepared sauce over the beef and vegetables. Cook for 2-3 minutes, stirring frequently, until the sauce thickens and everything is evenly coated.

Serve: Remove from heat and serve the Pineapple Beef and Broccoli Stir-Fry hot over a bed of steamed rice. Garnish with additional fresh pineapple or sesame seeds if desired.