For the Steak: Add 1 ½ teaspoons sesame oil and 1 tablespoon avocado oil to skillet or wok used to cook fried rice. Heat skillet over medium-high heat, swirling and tilting pan to distribute oil across entire surface, until oil is hot and shimmery.
For the Vegetables: Add 1 ½ teaspoons sesame oil and 1 tablespoon avocado oil to separate skillet or wok. Heat skillet over medium-high heat, swirling and tilting pan to distribute oil across entire surface, until oil is hot and shimmery.
For the Steak: When oil is hot, add 1 pound lean steak, 1 tablespoon soy sauce, 1 tablespoon butter, 2 teaspoons fresh lemon juice, salt, and freshly cracked black pepper to pan. Stir to incorporate ingredients, coating steak completely in liquids, salt, and pepper.
For the Vegetables: When oil is hot, add 1 large white onion, 2 cups baby bella mushrooms, 1 large zucchini, 1 tablespoon butter, 1 tablespoon soy sauce, salt, and freshly cracked black pepper to pan. Stir to incorporate ingredients, coating vegetables completely in liquids, salt, and pepper.
For the Steak: Cook steak 2 to 5 minutes (see Notes) until desired doneness is achieved, stirring or flipping steak occasionally to brown all sides. When steak is cooked as desired, transfer steak to plate or cutting board and set aside to rest 3 to 5 minutes.
For the Vegetables: Sauté vegetables, stirring occasionally, until vegetables are tender and can be easily pierced with tines of fork, approximately 6 to 8 minutes. Once tender, remove skillet from heat and set aside.