Prepare the Easy Stir Fry Sauce according to its recipe and set it nearby.
Pat the 1 lb beef sirloin strips dry with paper towels (optional) and cut into 2-inch strips if not already done.
Heat 2 Tbsp coconut oil or avocado oil in a large wok or skillet over medium-high heat until hot and shimmering.
Add the beef in a single layer if possible (cook in batches if the pan is crowded). Stir and cook until browned, about 3 to 4 minutes.
Move the beef to the side of the wok (or transfer to a plate) and keep the heat at medium-high.
Add the vegetables: 2 large carrots (chopped), 1 large crown broccoli (florets), 1 yellow squash (chopped), 1 zucchini squash (chopped), 1/2 red bell pepper (cored and cut into matchsticks), and 1/2 red onion (sliced). Cook and stir the vegetables for about 2 minutes.
Stir the beef back into the vegetables to combine.
Pour 1/4 to 1/3 cup of the prepared Easy Stir Fry Sauce into the wok. Cook, stirring constantly, until the sauce thickens and evenly coats the beef and vegetables, about 3 minutes. Taste and add more sauce if desired.
Serve the stir fry immediately.