Make the marinade. Combine olive or avocado oil, coconut aminos, minced garlic, vinegar, mustard, red pepper flakes, and fish sauce in a bowl and whisk to combine. Add steak cubes, toss to coat, and cover the bowl with some foil or plastic wrap. You can also use a sealed plastic bag instead of a bowl to marinate the steak. Let the steak marinate for 3-4 hours or more.
Preheat your grill to medium high heat. Time to assemble the kabobs! Grab your skewers, the cubed steak (set marinade aside, as we will brush everything with it before grilling), onions, pineapple, and peppers. Thread 3-4 pieces of each item onto each skewer.
Brush each uncooked kabob with some of the marinade.
Grill for 3-4 minutes each side, keeping a close eye on the steak. Brush with additional marinade halfway through cooking. Serve with cauliflower rice or regular rice and enjoy!