Prepare the cauliflower rice by sautéing lightly in a pan for 3–4 minutes, or keep raw for a fresh texture.
Slice the avocado, cucumber, and radishes; set aside.
If using seared tuna, heat a skillet over medium-high, sear tuna for 1–2 minutes per side, then slice thinly.
Whisk together soy sauce, sesame oil, rice vinegar, sweetener, and red pepper flakes to make the dressing.
Assemble bowls by layering cauliflower rice, tuna slices, avocado, cucumber, and radishes.
Drizzle dressing over the top, sprinkle with sesame seeds and green onions, and serve immediately.