PREHEAT the oven to 350℉. Arrange the walnuts in a single layer on a large rimmed baking sheet. Bake, stirring once, until fragrant and golden, 5 to 8 minutes. Let cool.
IN a food processor, combined the toasted walnuts, the black beans, cauliflower, nutritional yeast, avocado oil, chili powder, cumin, oregano, and salt. Pulse until nuts are finely chopped and mixture is combined (be careful to not overprocess).
IN a large skillet, heat the olive oil over medium heat. Add the cauliflower mixture and cook until heated through, 3 to 5 minutes.
DIVIDE the salad greens among three serving plates and top with the crumble. Drizzle with the dressing and sprinkle with the pepitas.