Add coconut oil to a large saucepan over medium heat. Sauté the onions & garlic for a few minutes until fragrant & softened. Increase heat to medium-high, add steak. Let it brown about 4 minutes, toss with tongs a few times to brown each side. Add coconut milk, red curry paste & salt to the pan.
Combine everything well. Cook uncovered for another 5 minutes and the sauce will thicken.
Assemble the tacos. Lay tortillas out, top with lettuce, steak, avocado & green onion. Serve immediately. If there is extra sauce in the pan be sure to spoon some on top!