Tenderize the sirloin steak by dusting it thoroughly with baking soda. Let it sit in the refrigerator for 25 minutes. Wash off the baking soda very well. Then, thoroughly pat the steak dry.

During this time, in a small bowl, make the sauce. Just mix the water with the cornstarch first (whisk so the cornstarch dissolves). Then, add the tomato paste, miso paste, soy sauce, onion powder, and paprika. Whisk until the sauce is smooth. Set aside.

Slice the sirloin steak into small cubes (like they do at Panda Express). Sprinkle salt over the steak and set it aside.

Heat the pan or wok to medium heat. Add oil. Next, add the chopped onions, garlic, and then the mushrooms. Pour a few tablespoons of water into the pan, cover with the lid, and cook for two minutes. This allows the mushrooms to cook faster.

Then remove the lid and add the bell pepper and broccolini stems. Mix and toss. Lastly, add the broccolini florets and toss in. Remove the vegetable mix to a bowl and set aside. The veggies should be colorful and crisp.

Next, clean the pan and reheat over medium-high heat and add a little avocado oil. Set the steak in the pan evenly, so the steak will sear and brown (3 minutes). Do not touch the steak so it can sear. Flip the steak pieces to finish searing (additional 1-2 minutes). If your pan is not too big, sear the steak in batches to avoid steaming.

Immediately, as the steak looks seared and has cooked for 4-5 minutes (it's fast), add the sauce. The sauce should be simmering for one minute.

Return the vegetable mixture to the skillet and toss everything together until coated and glossy. Sprinkle black pepper and chili flakes and toss. Serve hot and enjoy!