Heat Macadamia nut oil in a large skillet over medium-high heat. Cook onion, and red pepper in the oil until onion is tender and golden, and peppers are slightly soft, about 10 minutes. Stir balsamic vinegar into the vegetables; season with salt and pepper.
Rub tilapia filets with 2 teaspoons Macadamia nut oil, sesame seeds and a sprinkle of salt and pepper. Place fillets in a small baking dish, and top with the balsamic onion mixture. Sprinkle fish evenly with cheese.
Bake in preheated oven until fish flakes easily. Serve atop potatoes.