Preheat oven to 425°. On a large baking sheet, toss cauliflower, shallots, chili powder, cumin, and 2 tablespoons oil until coated; season with salt and pepper.
Bake until cauliflower is golden and crisp and shallots are tender, 30 to 35 minutes. Let cool slightly, then slice shallots into rings.
Meanwhile, in a blender or food processor, blend avocado, water, vinegar, lime juice, ¼ cup parsley, and remaining 2 tablespoons oil until smooth; season with salt and pepper. If needed, add more water, 1 tablespoon at a time, to make a thinner dressing. Refrigerate until ready to use.
In a large bowl, combine romaine, spinach, and remaining ¼ cup parsley. Add cauliflower, shallots, tomatoes, Parmesan, and almonds and toss to combine. Add desired amount of dressing and toss again to coat.
Make Ahead: Dressing can be made 1 day ahead. Store in an airtight container and refrigerate.