Heat the peanut oil in a large skillet over medium heat until the oil just begins to smoke; cook and stir the onion, garlic, and salt in the hot oil until the onions are translucent, about 2 minutes. Stir the watermelon rind, red bell pepper, and about half the vegetable broth into the onion mixture. Reduce heat to low. Place a cover over the skillet and simmer the mixture for 5 minutes.
Whisk the remaining vegetable broth, the teriyaki sauce, and cornstarch together in a small bowl; stir into the mixture in the skillet and cook until the mixture begins to thicken. Serve hot.
