Whisk the Pear (3/4 cup), Yellow Onion (1/2 cup), Garlic (6 clove), Fresh Ginger (1/2 teaspoon), Low-Sodium Soy Sauce (1/2 cup), Dark Brown Sugar (1/2 cup), Sweet Chili Sauce (1/4 cup), and Crushed Red Pepper Flakes (1/2 tablespoon) together in a small bowl.
Divide the sauce: 1/3 for the marinade, and 2/3 for the glaze.
Combine 1/3 of the Korean Barbecue Sauce together with the Toasted Sesame Oil (1/4 cup); this is your marinade. Reserve and refrigerate remaining Korean Barbecue Sauce.
Place Beef Tenderloin (2 pound) in a large freezer bag and pour the marinade over the top. Seal bag and gently squeeze/toss to coat. Refrigerate for at least 4 to 6 hours.
Place the remaining Korean Barbecue Sauce into a small saucepan over medium-low heat until it just starts to simmer.
Mix Corn Starch (1 tablespoon) and Water (3 tablespoon) together and pour mixture into the pan, stirring constantly. Continue to simmer for 5 minutes, stirring occasionally.
While it is simmering, give it a taste, and if you want it a little bit hotter, add another teaspoon of red pepper flakes or Sriracha. If you want it sweeter, add brown sugar to taste. Remove from heat. Sauce will thicken as it cools.
If grilling, grease and preheat grill to medium-high heat.
If using wooden skewers, soak in water for at least 30 minutes before grilling or broiling. If using metal skewers, skewer away. Thread marinated beef and Red Bell Pepper (2), Orange Bell Pepper (2), Yellow Bell Pepper (2), and Red Onion (1) onto skewers.
Grill kabobs until lightly charred all over, approximately 2-3 minutes per side, brushing lightly with half of the Korean Barbebue Sauce. You can check the meat cubes for doneness if desired - you don't want to overcook.
Let rest 5 minutes before serving. Serve with reserved Korean Barbecue Glaze.
OVEN INSTRUCTIONS: Preheat oven to 450 degrees F (230 degrees C). Line a rimmed baking sheet with foil for easy clean up. Lightly spray with nonstick cooking spray.
Evenly space kabobs on baking sheet, brush with half of the Korean Barbecue Glaze and bake 12-16 minutes, turning once OR until meat reaches desired doneness (cooking time will vary depending on each side, so you can check a chunk of the meat for doneness if desired).
Let rest 5 minutes before serving. Serve with reserved Korean Barbeque Glaze.