In a small bowl, whisk together the olive oil, lime juice, minced garlic, cumin, chili powder, salt, and pepper to create the marinade.
Place the flank steak in a shallow dish or resealable bag, pour the marinade over it, and let it sit for at least 30 minutes in the refrigerator.
While the steak marinates, prepare the salsa by combining the diced avocado, tomato, red onion, and cilantro in a small bowl.
Preheat a grill or cast-iron grill pan over medium-high heat and lightly coat with a touch of oil.
Grill the steak for 4-5 minutes per side for medium-rare, or until it reaches your desired level of doneness.
Remove the steak from the heat and let it rest on a cutting board for 5-10 minutes to keep the juices locked in.
While the steak rests, lightly sauté the cauliflower rice in a pan with a splash of water or lime juice until tender.
Slice the steak against the grain into thin strips and serve over the cauliflower rice, topped with the fresh avocado salsa.